Chapter 25: Subtraction within 20
Learn Grade 1 mathematics from very beginner explanations through worked examples, practice, reasoning, and review.
Chapter Overview
This chapter teaches Subtraction within 20 with simple language, step-by-step reasoning, and original worked examples. Math words are explained in simple Grade 1 language.
Key Technical Terms
- Subtracting from teen numbers (a Grade 1 idea used in this chapter)
- Subtracting a single digit (a Grade 1 idea used in this chapter)
- Counting back within 20 (a Grade 1 idea used in this chapter)
- Using make-10 ideas (a Grade 1 idea used in this chapter)
- Using ten frames (a Grade 1 idea used in this chapter)
- Using number lines (a Grade 1 idea used in this chapter)
- Finding the missing part (a Grade 1 idea used in this chapter)
- Subtraction stories within 20 (a Grade 1 idea used in this chapter)
- Checking with addition (a Grade 1 idea used in this chapter)
- Subtraction within 20 review (a Grade 1 idea used in this chapter)
How to Learn This Chapter
Read or listen to the explanation, use objects or pictures when helpful, follow one step at a time, and try the example again before checking the answer.
25.1 Subtracting from teen numbers
Subtracting from teen numbers helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Beginner Note
Start with real objects, fingers, or a picture. Say the idea aloud, try one small example, and check it by counting or comparing again.
10 Worked Examples with Answers and Very-Beginner Explanations
Worked Example 1
Problem: What does Subtracting from teen numbers mean?
- Say the topic in simple words.
- Use objects, fingers, a drawing, or a number example.
- Tell what you notice.
Very beginner explanation: Subtracting from teen numbers helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Answer: Subtracting from teen numbers helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Worked Example 2
Problem: Show one small example of Subtracting from teen numbers.
- Choose small numbers or a simple shape/object.
- Make a model or drawing.
- Describe what the model shows.
Very beginner explanation: Subtracting from teen numbers helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Answer: A correct small model or drawing can show the meaning of Subtracting from teen numbers.
Worked Example 3
Problem: Which tool could help with Subtracting from teen numbers?
- Think about counters, fingers, a ten frame, number line, picture, table, or real object.
- Choose the tool that makes the idea easiest to see.
Very beginner explanation: Subtracting from teen numbers helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Answer: Use a simple tool that lets you see and check the quantities or shapes.
Worked Example 4
Problem: How can you check your work in Subtracting from teen numbers?
- Look at the objects, drawing, or numbers again.
- Count or compare one more time.
- Make sure the answer matches the question.
Very beginner explanation: Subtracting from teen numbers helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Answer: Check by recounting, comparing, or using a second simple model.
Worked Example 5
Problem: Where might you use Subtracting from teen numbers in everyday life?
- Think about toys, snacks, books, classroom objects, calendars, shapes, or money.
- Choose one situation.
- Explain how the math helps.
Very beginner explanation: Subtracting from teen numbers helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Answer: Subtracting from teen numbers can help with a simple everyday task such as counting, sharing, comparing, measuring, organizing, or deciding.
Worked Example 6
Problem: Count to 6. What number comes just before 6?
- Count forward until 6.
- Move back one number.
Very beginner explanation: The number before is one less.
Answer: 5
Worked Example 7
Problem: Count to 12. What number comes just before 12?
- Count forward until 12.
- Move back one number.
Very beginner explanation: The number before is one less.
Answer: 11
Worked Example 8
Problem: Count to 19. What number comes just before 19?
- Count forward until 19.
- Move back one number.
Very beginner explanation: The number before is one less.
Answer: 18
Worked Example 9
Problem: Count to 27. What number comes just before 27?
- Count forward until 27.
- Move back one number.
Very beginner explanation: The number before is one less.
Answer: 26
Worked Example 10
Problem: Count to 44. What number comes just before 44?
- Count forward until 44.
- Move back one number.
Very beginner explanation: The number before is one less.
Answer: 43
Practice Exercise
Create one small question about Subtracting from teen numbers. Show it with objects, a picture, or numbers, then check by counting or comparing again.
25.2 Subtracting a single digit
Subtracting a single digit teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Beginner Note
Start with real objects, fingers, or a picture. Say the idea aloud, try one small example, and check it by counting or comparing again.
10 Worked Examples with Answers and Very-Beginner Explanations
Worked Example 1
Problem: What does Subtracting a single digit mean?
- Say the topic in simple words.
- Use objects, fingers, a drawing, or a number example.
- Tell what you notice.
Very beginner explanation: Subtracting a single digit teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Answer: Subtracting a single digit teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Worked Example 2
Problem: Show one small example of Subtracting a single digit.
- Choose small numbers or a simple shape/object.
- Make a model or drawing.
- Describe what the model shows.
Very beginner explanation: Subtracting a single digit teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Answer: A correct small model or drawing can show the meaning of Subtracting a single digit.
Worked Example 3
Problem: Which tool could help with Subtracting a single digit?
- Think about counters, fingers, a ten frame, number line, picture, table, or real object.
- Choose the tool that makes the idea easiest to see.
Very beginner explanation: Subtracting a single digit teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Answer: Use a simple tool that lets you see and check the quantities or shapes.
Worked Example 4
Problem: How can you check your work in Subtracting a single digit?
- Look at the objects, drawing, or numbers again.
- Count or compare one more time.
- Make sure the answer matches the question.
Very beginner explanation: Subtracting a single digit teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Answer: Check by recounting, comparing, or using a second simple model.
Worked Example 5
Problem: Where might you use Subtracting a single digit in everyday life?
- Think about toys, snacks, books, classroom objects, calendars, shapes, or money.
- Choose one situation.
- Explain how the math helps.
Very beginner explanation: Subtracting a single digit teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Answer: Subtracting a single digit can help with a simple everyday task such as counting, sharing, comparing, measuring, organizing, or deciding.
Worked Example 6
Problem: Find 5 - 2.
- Start with 5 objects.
- Take away 2.
- Count what is left.
Very beginner explanation: Subtraction tells how many are left or the difference.
Answer: 3
Worked Example 7
Problem: Find 7 - 3.
- Start with 7 objects.
- Take away 3.
- Count what is left.
Very beginner explanation: Subtraction tells how many are left or the difference.
Answer: 4
Worked Example 8
Problem: Find 9 - 4.
- Start with 9 objects.
- Take away 4.
- Count what is left.
Very beginner explanation: Subtraction tells how many are left or the difference.
Answer: 5
Worked Example 9
Problem: Find 10 - 6.
- Start with 10 objects.
- Take away 6.
- Count what is left.
Very beginner explanation: Subtraction tells how many are left or the difference.
Answer: 4
Worked Example 10
Problem: Find 14 - 5.
- Start with 14 objects.
- Take away 5.
- Count what is left.
Very beginner explanation: Subtraction tells how many are left or the difference.
Answer: 9
Practice Exercise
Create one small question about Subtracting a single digit. Show it with objects, a picture, or numbers, then check by counting or comparing again.
25.3 Counting back within 20
Counting back within 20 helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Beginner Note
Start with real objects, fingers, or a picture. Say the idea aloud, try one small example, and check it by counting or comparing again.
10 Worked Examples with Answers and Very-Beginner Explanations
Worked Example 1
Problem: What does Counting back within 20 mean?
- Say the topic in simple words.
- Use objects, fingers, a drawing, or a number example.
- Tell what you notice.
Very beginner explanation: Counting back within 20 helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Answer: Counting back within 20 helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Worked Example 2
Problem: Show one small example of Counting back within 20.
- Choose small numbers or a simple shape/object.
- Make a model or drawing.
- Describe what the model shows.
Very beginner explanation: Counting back within 20 helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Answer: A correct small model or drawing can show the meaning of Counting back within 20.
Worked Example 3
Problem: Which tool could help with Counting back within 20?
- Think about counters, fingers, a ten frame, number line, picture, table, or real object.
- Choose the tool that makes the idea easiest to see.
Very beginner explanation: Counting back within 20 helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Answer: Use a simple tool that lets you see and check the quantities or shapes.
Worked Example 4
Problem: How can you check your work in Counting back within 20?
- Look at the objects, drawing, or numbers again.
- Count or compare one more time.
- Make sure the answer matches the question.
Very beginner explanation: Counting back within 20 helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Answer: Check by recounting, comparing, or using a second simple model.
Worked Example 5
Problem: Where might you use Counting back within 20 in everyday life?
- Think about toys, snacks, books, classroom objects, calendars, shapes, or money.
- Choose one situation.
- Explain how the math helps.
Very beginner explanation: Counting back within 20 helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Answer: Counting back within 20 can help with a simple everyday task such as counting, sharing, comparing, measuring, organizing, or deciding.
Worked Example 6
Problem: Count to 6. What number comes just before 6?
- Count forward until 6.
- Move back one number.
Very beginner explanation: The number before is one less.
Answer: 5
Worked Example 7
Problem: Count to 12. What number comes just before 12?
- Count forward until 12.
- Move back one number.
Very beginner explanation: The number before is one less.
Answer: 11
Worked Example 8
Problem: Count to 19. What number comes just before 19?
- Count forward until 19.
- Move back one number.
Very beginner explanation: The number before is one less.
Answer: 18
Worked Example 9
Problem: Count to 27. What number comes just before 27?
- Count forward until 27.
- Move back one number.
Very beginner explanation: The number before is one less.
Answer: 26
Worked Example 10
Problem: Count to 44. What number comes just before 44?
- Count forward until 44.
- Move back one number.
Very beginner explanation: The number before is one less.
Answer: 43
Practice Exercise
Create one small question about Counting back within 20. Show it with objects, a picture, or numbers, then check by counting or comparing again.
25.4 Using make-10 ideas
Using make-10 ideas is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Beginner Note
Start with real objects, fingers, or a picture. Say the idea aloud, try one small example, and check it by counting or comparing again.
10 Worked Examples with Answers and Very-Beginner Explanations
Worked Example 1
Problem: What does Using make-10 ideas mean?
- Say the topic in simple words.
- Use objects, fingers, a drawing, or a number example.
- Tell what you notice.
Very beginner explanation: Using make-10 ideas is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Answer: Using make-10 ideas is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Worked Example 2
Problem: Show one small example of Using make-10 ideas.
- Choose small numbers or a simple shape/object.
- Make a model or drawing.
- Describe what the model shows.
Very beginner explanation: Using make-10 ideas is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Answer: A correct small model or drawing can show the meaning of Using make-10 ideas.
Worked Example 3
Problem: Which tool could help with Using make-10 ideas?
- Think about counters, fingers, a ten frame, number line, picture, table, or real object.
- Choose the tool that makes the idea easiest to see.
Very beginner explanation: Using make-10 ideas is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Answer: Use a simple tool that lets you see and check the quantities or shapes.
Worked Example 4
Problem: How can you check your work in Using make-10 ideas?
- Look at the objects, drawing, or numbers again.
- Count or compare one more time.
- Make sure the answer matches the question.
Very beginner explanation: Using make-10 ideas is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Answer: Check by recounting, comparing, or using a second simple model.
Worked Example 5
Problem: Where might you use Using make-10 ideas in everyday life?
- Think about toys, snacks, books, classroom objects, calendars, shapes, or money.
- Choose one situation.
- Explain how the math helps.
Very beginner explanation: Using make-10 ideas is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Answer: Using make-10 ideas can help with a simple everyday task such as counting, sharing, comparing, measuring, organizing, or deciding.
Worked Example 6
Problem: Show Using make-10 ideas with a simple Grade 1 example.
- Use small numbers, objects, or a drawing.
- Explain what the example shows.
Very beginner explanation: Grade 1 learners understand Using make-10 ideas best through concrete examples and clear words.
Answer: A correct simple example of Using make-10 ideas.
Worked Example 7
Problem: Show Using make-10 ideas with a simple Grade 1 example.
- Use small numbers, objects, or a drawing.
- Explain what the example shows.
Very beginner explanation: Grade 1 learners understand Using make-10 ideas best through concrete examples and clear words.
Answer: A correct simple example of Using make-10 ideas.
Worked Example 8
Problem: Show Using make-10 ideas with a simple Grade 1 example.
- Use small numbers, objects, or a drawing.
- Explain what the example shows.
Very beginner explanation: Grade 1 learners understand Using make-10 ideas best through concrete examples and clear words.
Answer: A correct simple example of Using make-10 ideas.
Worked Example 9
Problem: Show Using make-10 ideas with a simple Grade 1 example.
- Use small numbers, objects, or a drawing.
- Explain what the example shows.
Very beginner explanation: Grade 1 learners understand Using make-10 ideas best through concrete examples and clear words.
Answer: A correct simple example of Using make-10 ideas.
Worked Example 10
Problem: Show Using make-10 ideas with a simple Grade 1 example.
- Use small numbers, objects, or a drawing.
- Explain what the example shows.
Very beginner explanation: Grade 1 learners understand Using make-10 ideas best through concrete examples and clear words.
Answer: A correct simple example of Using make-10 ideas.
Practice Exercise
Create one small question about Using make-10 ideas. Show it with objects, a picture, or numbers, then check by counting or comparing again.
25.5 Using ten frames
Using ten frames is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Beginner Note
Start with real objects, fingers, or a picture. Say the idea aloud, try one small example, and check it by counting or comparing again.
10 Worked Examples with Answers and Very-Beginner Explanations
Worked Example 1
Problem: What does Using ten frames mean?
- Say the topic in simple words.
- Use objects, fingers, a drawing, or a number example.
- Tell what you notice.
Very beginner explanation: Using ten frames is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Answer: Using ten frames is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Worked Example 2
Problem: Show one small example of Using ten frames.
- Choose small numbers or a simple shape/object.
- Make a model or drawing.
- Describe what the model shows.
Very beginner explanation: Using ten frames is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Answer: A correct small model or drawing can show the meaning of Using ten frames.
Worked Example 3
Problem: Which tool could help with Using ten frames?
- Think about counters, fingers, a ten frame, number line, picture, table, or real object.
- Choose the tool that makes the idea easiest to see.
Very beginner explanation: Using ten frames is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Answer: Use a simple tool that lets you see and check the quantities or shapes.
Worked Example 4
Problem: How can you check your work in Using ten frames?
- Look at the objects, drawing, or numbers again.
- Count or compare one more time.
- Make sure the answer matches the question.
Very beginner explanation: Using ten frames is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Answer: Check by recounting, comparing, or using a second simple model.
Worked Example 5
Problem: Where might you use Using ten frames in everyday life?
- Think about toys, snacks, books, classroom objects, calendars, shapes, or money.
- Choose one situation.
- Explain how the math helps.
Very beginner explanation: Using ten frames is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Answer: Using ten frames can help with a simple everyday task such as counting, sharing, comparing, measuring, organizing, or deciding.
Worked Example 6
Problem: Show Using ten frames with a simple Grade 1 example.
- Use small numbers, objects, or a drawing.
- Explain what the example shows.
Very beginner explanation: Grade 1 learners understand Using ten frames best through concrete examples and clear words.
Answer: A correct simple example of Using ten frames.
Worked Example 7
Problem: Show Using ten frames with a simple Grade 1 example.
- Use small numbers, objects, or a drawing.
- Explain what the example shows.
Very beginner explanation: Grade 1 learners understand Using ten frames best through concrete examples and clear words.
Answer: A correct simple example of Using ten frames.
Worked Example 8
Problem: Show Using ten frames with a simple Grade 1 example.
- Use small numbers, objects, or a drawing.
- Explain what the example shows.
Very beginner explanation: Grade 1 learners understand Using ten frames best through concrete examples and clear words.
Answer: A correct simple example of Using ten frames.
Worked Example 9
Problem: Show Using ten frames with a simple Grade 1 example.
- Use small numbers, objects, or a drawing.
- Explain what the example shows.
Very beginner explanation: Grade 1 learners understand Using ten frames best through concrete examples and clear words.
Answer: A correct simple example of Using ten frames.
Worked Example 10
Problem: Show Using ten frames with a simple Grade 1 example.
- Use small numbers, objects, or a drawing.
- Explain what the example shows.
Very beginner explanation: Grade 1 learners understand Using ten frames best through concrete examples and clear words.
Answer: A correct simple example of Using ten frames.
Practice Exercise
Create one small question about Using ten frames. Show it with objects, a picture, or numbers, then check by counting or comparing again.
25.6 Using number lines
Using number lines helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Beginner Note
Start with real objects, fingers, or a picture. Say the idea aloud, try one small example, and check it by counting or comparing again.
10 Worked Examples with Answers and Very-Beginner Explanations
Worked Example 1
Problem: What does Using number lines mean?
- Say the topic in simple words.
- Use objects, fingers, a drawing, or a number example.
- Tell what you notice.
Very beginner explanation: Using number lines helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Answer: Using number lines helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Worked Example 2
Problem: Show one small example of Using number lines.
- Choose small numbers or a simple shape/object.
- Make a model or drawing.
- Describe what the model shows.
Very beginner explanation: Using number lines helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Answer: A correct small model or drawing can show the meaning of Using number lines.
Worked Example 3
Problem: Which tool could help with Using number lines?
- Think about counters, fingers, a ten frame, number line, picture, table, or real object.
- Choose the tool that makes the idea easiest to see.
Very beginner explanation: Using number lines helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Answer: Use a simple tool that lets you see and check the quantities or shapes.
Worked Example 4
Problem: How can you check your work in Using number lines?
- Look at the objects, drawing, or numbers again.
- Count or compare one more time.
- Make sure the answer matches the question.
Very beginner explanation: Using number lines helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Answer: Check by recounting, comparing, or using a second simple model.
Worked Example 5
Problem: Where might you use Using number lines in everyday life?
- Think about toys, snacks, books, classroom objects, calendars, shapes, or money.
- Choose one situation.
- Explain how the math helps.
Very beginner explanation: Using number lines helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Answer: Using number lines can help with a simple everyday task such as counting, sharing, comparing, measuring, organizing, or deciding.
Worked Example 6
Problem: Count to 6. What number comes just before 6?
- Count forward until 6.
- Move back one number.
Very beginner explanation: The number before is one less.
Answer: 5
Worked Example 7
Problem: Count to 12. What number comes just before 12?
- Count forward until 12.
- Move back one number.
Very beginner explanation: The number before is one less.
Answer: 11
Worked Example 8
Problem: Count to 19. What number comes just before 19?
- Count forward until 19.
- Move back one number.
Very beginner explanation: The number before is one less.
Answer: 18
Worked Example 9
Problem: Count to 27. What number comes just before 27?
- Count forward until 27.
- Move back one number.
Very beginner explanation: The number before is one less.
Answer: 26
Worked Example 10
Problem: Count to 44. What number comes just before 44?
- Count forward until 44.
- Move back one number.
Very beginner explanation: The number before is one less.
Answer: 43
Practice Exercise
Create one small question about Using number lines. Show it with objects, a picture, or numbers, then check by counting or comparing again.
25.7 Finding the missing part
Finding the missing part is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Beginner Note
Start with real objects, fingers, or a picture. Say the idea aloud, try one small example, and check it by counting or comparing again.
10 Worked Examples with Answers and Very-Beginner Explanations
Worked Example 1
Problem: What does Finding the missing part mean?
- Say the topic in simple words.
- Use objects, fingers, a drawing, or a number example.
- Tell what you notice.
Very beginner explanation: Finding the missing part is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Answer: Finding the missing part is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Worked Example 2
Problem: Show one small example of Finding the missing part.
- Choose small numbers or a simple shape/object.
- Make a model or drawing.
- Describe what the model shows.
Very beginner explanation: Finding the missing part is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Answer: A correct small model or drawing can show the meaning of Finding the missing part.
Worked Example 3
Problem: Which tool could help with Finding the missing part?
- Think about counters, fingers, a ten frame, number line, picture, table, or real object.
- Choose the tool that makes the idea easiest to see.
Very beginner explanation: Finding the missing part is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Answer: Use a simple tool that lets you see and check the quantities or shapes.
Worked Example 4
Problem: How can you check your work in Finding the missing part?
- Look at the objects, drawing, or numbers again.
- Count or compare one more time.
- Make sure the answer matches the question.
Very beginner explanation: Finding the missing part is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Answer: Check by recounting, comparing, or using a second simple model.
Worked Example 5
Problem: Where might you use Finding the missing part in everyday life?
- Think about toys, snacks, books, classroom objects, calendars, shapes, or money.
- Choose one situation.
- Explain how the math helps.
Very beginner explanation: Finding the missing part is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Answer: Finding the missing part can help with a simple everyday task such as counting, sharing, comparing, measuring, organizing, or deciding.
Worked Example 6
Problem: Show Finding the missing part with a simple Grade 1 example.
- Use small numbers, objects, or a drawing.
- Explain what the example shows.
Very beginner explanation: Grade 1 learners understand Finding the missing part best through concrete examples and clear words.
Answer: A correct simple example of Finding the missing part.
Worked Example 7
Problem: Show Finding the missing part with a simple Grade 1 example.
- Use small numbers, objects, or a drawing.
- Explain what the example shows.
Very beginner explanation: Grade 1 learners understand Finding the missing part best through concrete examples and clear words.
Answer: A correct simple example of Finding the missing part.
Worked Example 8
Problem: Show Finding the missing part with a simple Grade 1 example.
- Use small numbers, objects, or a drawing.
- Explain what the example shows.
Very beginner explanation: Grade 1 learners understand Finding the missing part best through concrete examples and clear words.
Answer: A correct simple example of Finding the missing part.
Worked Example 9
Problem: Show Finding the missing part with a simple Grade 1 example.
- Use small numbers, objects, or a drawing.
- Explain what the example shows.
Very beginner explanation: Grade 1 learners understand Finding the missing part best through concrete examples and clear words.
Answer: A correct simple example of Finding the missing part.
Worked Example 10
Problem: Show Finding the missing part with a simple Grade 1 example.
- Use small numbers, objects, or a drawing.
- Explain what the example shows.
Very beginner explanation: Grade 1 learners understand Finding the missing part best through concrete examples and clear words.
Answer: A correct simple example of Finding the missing part.
Practice Exercise
Create one small question about Finding the missing part. Show it with objects, a picture, or numbers, then check by counting or comparing again.
25.8 Subtraction stories within 20
Subtraction stories within 20 teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Beginner Note
Start with real objects, fingers, or a picture. Say the idea aloud, try one small example, and check it by counting or comparing again.
10 Worked Examples with Answers and Very-Beginner Explanations
Worked Example 1
Problem: What does Subtraction stories within 20 mean?
- Say the topic in simple words.
- Use objects, fingers, a drawing, or a number example.
- Tell what you notice.
Very beginner explanation: Subtraction stories within 20 teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Answer: Subtraction stories within 20 teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Worked Example 2
Problem: Show one small example of Subtraction stories within 20.
- Choose small numbers or a simple shape/object.
- Make a model or drawing.
- Describe what the model shows.
Very beginner explanation: Subtraction stories within 20 teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Answer: A correct small model or drawing can show the meaning of Subtraction stories within 20.
Worked Example 3
Problem: Which tool could help with Subtraction stories within 20?
- Think about counters, fingers, a ten frame, number line, picture, table, or real object.
- Choose the tool that makes the idea easiest to see.
Very beginner explanation: Subtraction stories within 20 teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Answer: Use a simple tool that lets you see and check the quantities or shapes.
Worked Example 4
Problem: How can you check your work in Subtraction stories within 20?
- Look at the objects, drawing, or numbers again.
- Count or compare one more time.
- Make sure the answer matches the question.
Very beginner explanation: Subtraction stories within 20 teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Answer: Check by recounting, comparing, or using a second simple model.
Worked Example 5
Problem: Where might you use Subtraction stories within 20 in everyday life?
- Think about toys, snacks, books, classroom objects, calendars, shapes, or money.
- Choose one situation.
- Explain how the math helps.
Very beginner explanation: Subtraction stories within 20 teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Answer: Subtraction stories within 20 can help with a simple everyday task such as counting, sharing, comparing, measuring, organizing, or deciding.
Worked Example 6
Problem: Find 5 - 2.
- Start with 5 objects.
- Take away 2.
- Count what is left.
Very beginner explanation: Subtraction tells how many are left or the difference.
Answer: 3
Worked Example 7
Problem: Find 7 - 3.
- Start with 7 objects.
- Take away 3.
- Count what is left.
Very beginner explanation: Subtraction tells how many are left or the difference.
Answer: 4
Worked Example 8
Problem: Find 9 - 4.
- Start with 9 objects.
- Take away 4.
- Count what is left.
Very beginner explanation: Subtraction tells how many are left or the difference.
Answer: 5
Worked Example 9
Problem: Find 10 - 6.
- Start with 10 objects.
- Take away 6.
- Count what is left.
Very beginner explanation: Subtraction tells how many are left or the difference.
Answer: 4
Worked Example 10
Problem: Find 14 - 5.
- Start with 14 objects.
- Take away 5.
- Count what is left.
Very beginner explanation: Subtraction tells how many are left or the difference.
Answer: 9
Practice Exercise
Create one small question about Subtraction stories within 20. Show it with objects, a picture, or numbers, then check by counting or comparing again.
25.9 Checking with addition
Checking with addition teaches how to put quantities together. Learners use objects, drawings, ten frames, and counting-on strategies before writing number sentences.
Beginner Note
Start with real objects, fingers, or a picture. Say the idea aloud, try one small example, and check it by counting or comparing again.
10 Worked Examples with Answers and Very-Beginner Explanations
Worked Example 1
Problem: What does Checking with addition mean?
- Say the topic in simple words.
- Use objects, fingers, a drawing, or a number example.
- Tell what you notice.
Very beginner explanation: Checking with addition teaches how to put quantities together. Learners use objects, drawings, ten frames, and counting-on strategies before writing number sentences.
Answer: Checking with addition teaches how to put quantities together. Learners use objects, drawings, ten frames, and counting-on strategies before writing number sentences.
Worked Example 2
Problem: Show one small example of Checking with addition.
- Choose small numbers or a simple shape/object.
- Make a model or drawing.
- Describe what the model shows.
Very beginner explanation: Checking with addition teaches how to put quantities together. Learners use objects, drawings, ten frames, and counting-on strategies before writing number sentences.
Answer: A correct small model or drawing can show the meaning of Checking with addition.
Worked Example 3
Problem: Which tool could help with Checking with addition?
- Think about counters, fingers, a ten frame, number line, picture, table, or real object.
- Choose the tool that makes the idea easiest to see.
Very beginner explanation: Checking with addition teaches how to put quantities together. Learners use objects, drawings, ten frames, and counting-on strategies before writing number sentences.
Answer: Use a simple tool that lets you see and check the quantities or shapes.
Worked Example 4
Problem: How can you check your work in Checking with addition?
- Look at the objects, drawing, or numbers again.
- Count or compare one more time.
- Make sure the answer matches the question.
Very beginner explanation: Checking with addition teaches how to put quantities together. Learners use objects, drawings, ten frames, and counting-on strategies before writing number sentences.
Answer: Check by recounting, comparing, or using a second simple model.
Worked Example 5
Problem: Where might you use Checking with addition in everyday life?
- Think about toys, snacks, books, classroom objects, calendars, shapes, or money.
- Choose one situation.
- Explain how the math helps.
Very beginner explanation: Checking with addition teaches how to put quantities together. Learners use objects, drawings, ten frames, and counting-on strategies before writing number sentences.
Answer: Checking with addition can help with a simple everyday task such as counting, sharing, comparing, measuring, organizing, or deciding.
Worked Example 6
Problem: Find 2 + 3.
- Make a group of 2.
- Add 3 more.
- Count all the objects.
Very beginner explanation: Addition puts quantities together.
Answer: 5
Worked Example 7
Problem: Find 4 + 1.
- Make a group of 4.
- Add 1 more.
- Count all the objects.
Very beginner explanation: Addition puts quantities together.
Answer: 5
Worked Example 8
Problem: Find 5 + 2.
- Make a group of 5.
- Add 2 more.
- Count all the objects.
Very beginner explanation: Addition puts quantities together.
Answer: 7
Worked Example 9
Problem: Find 6 + 3.
- Make a group of 6.
- Add 3 more.
- Count all the objects.
Very beginner explanation: Addition puts quantities together.
Answer: 9
Worked Example 10
Problem: Find 8 + 2.
- Make a group of 8.
- Add 2 more.
- Count all the objects.
Very beginner explanation: Addition puts quantities together.
Answer: 10
Practice Exercise
Create one small question about Checking with addition. Show it with objects, a picture, or numbers, then check by counting or comparing again.
25.10 Subtraction within 20 review
Subtraction within 20 review teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Beginner Note
Start with real objects, fingers, or a picture. Say the idea aloud, try one small example, and check it by counting or comparing again.
10 Worked Examples with Answers and Very-Beginner Explanations
Worked Example 1
Problem: What does Subtraction within 20 review mean?
- Say the topic in simple words.
- Use objects, fingers, a drawing, or a number example.
- Tell what you notice.
Very beginner explanation: Subtraction within 20 review teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Answer: Subtraction within 20 review teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Worked Example 2
Problem: Show one small example of Subtraction within 20 review.
- Choose small numbers or a simple shape/object.
- Make a model or drawing.
- Describe what the model shows.
Very beginner explanation: Subtraction within 20 review teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Answer: A correct small model or drawing can show the meaning of Subtraction within 20 review.
Worked Example 3
Problem: Which tool could help with Subtraction within 20 review?
- Think about counters, fingers, a ten frame, number line, picture, table, or real object.
- Choose the tool that makes the idea easiest to see.
Very beginner explanation: Subtraction within 20 review teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Answer: Use a simple tool that lets you see and check the quantities or shapes.
Worked Example 4
Problem: How can you check your work in Subtraction within 20 review?
- Look at the objects, drawing, or numbers again.
- Count or compare one more time.
- Make sure the answer matches the question.
Very beginner explanation: Subtraction within 20 review teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Answer: Check by recounting, comparing, or using a second simple model.
Worked Example 5
Problem: Where might you use Subtraction within 20 review in everyday life?
- Think about toys, snacks, books, classroom objects, calendars, shapes, or money.
- Choose one situation.
- Explain how the math helps.
Very beginner explanation: Subtraction within 20 review teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Answer: Subtraction within 20 review can help with a simple everyday task such as counting, sharing, comparing, measuring, organizing, or deciding.
Worked Example 6
Problem: Find 5 - 2.
- Start with 5 objects.
- Take away 2.
- Count what is left.
Very beginner explanation: Subtraction tells how many are left or the difference.
Answer: 3
Worked Example 7
Problem: Find 7 - 3.
- Start with 7 objects.
- Take away 3.
- Count what is left.
Very beginner explanation: Subtraction tells how many are left or the difference.
Answer: 4
Worked Example 8
Problem: Find 9 - 4.
- Start with 9 objects.
- Take away 4.
- Count what is left.
Very beginner explanation: Subtraction tells how many are left or the difference.
Answer: 5
Worked Example 9
Problem: Find 10 - 6.
- Start with 10 objects.
- Take away 6.
- Count what is left.
Very beginner explanation: Subtraction tells how many are left or the difference.
Answer: 4
Worked Example 10
Problem: Find 14 - 5.
- Start with 14 objects.
- Take away 5.
- Count what is left.
Very beginner explanation: Subtraction tells how many are left or the difference.
Answer: 9
Practice Exercise
Create one small question about Subtraction within 20 review. Show it with objects, a picture, or numbers, then check by counting or comparing again.
Chapter Notes, Practice, and Common Mistakes
Chapter Notes
- Read or listen to the question before solving.
- Use objects, a drawing, ten frame, number line, table, graph, or simple number sentence when useful.
- Explain your thinking and check by counting, comparing, or using another simple model.
Extra Practice
- Create and solve one original problem about Subtracting from teen numbers.
- Create and solve one original problem about Subtracting a single digit.
- Create and solve one original problem about Counting back within 20.
- Create and solve one original problem about Using make-10 ideas.
- Create and solve one original problem about Using ten frames.
- Create and solve one original problem about Using number lines.
Common Mistakes
- Skipping the meaning and trying to memorize a rule only.
- Using the wrong operation because the question was not read completely.
- Ignoring units, labels, place values, or the context of the problem.
- Not estimating or checking whether the final answer is reasonable.
30 Review Questions and Answers
Q1. What is the main idea in Subtracting from teen numbers?
Answer: Subtracting from teen numbers helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Q2. What is the main idea in Subtracting a single digit?
Answer: Subtracting a single digit teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Q3. What is the main idea in Counting back within 20?
Answer: Counting back within 20 helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Q4. What is the main idea in Using make-10 ideas?
Answer: Using make-10 ideas is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Q5. What is the main idea in Using ten frames?
Answer: Using ten frames is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Q6. What is the main idea in Using number lines?
Answer: Using number lines helps Grade 1 learners build strong number sense with small numbers, objects, drawings, and number lines.
Q7. What is the main idea in Finding the missing part?
Answer: Finding the missing part is a Grade 1 mathematics idea. Learn it with objects or pictures first, then explain it with numbers or words.
Q8. What is the main idea in Subtraction stories within 20?
Answer: Subtraction stories within 20 teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Q9. What is the main idea in Checking with addition?
Answer: Checking with addition teaches how to put quantities together. Learners use objects, drawings, ten frames, and counting-on strategies before writing number sentences.
Q10. What is the main idea in Subtraction within 20 review?
Answer: Subtraction within 20 review teaches how to take away or find what is left. Learners use objects, drawings, and counting strategies to make the meaning clear.
Q11. Why is it useful to use counters or drawings?
Answer: They make the quantities visible and help you understand before using only numbers.
Q12. Why should you count carefully?
Answer: Careful counting means each object is counted once and no object is missed.
Q13. What can you do if a problem feels hard?
Answer: Use smaller numbers, draw a picture, use objects, and solve one small step at a time.
Q14. Why should both sides of an equals sign match?
Answer: The equals sign means the two sides have the same value.
Q15. How can a number line help?
Answer: It shows number order and can help you count forward or backward.
Q16. How can a ten frame help?
Answer: It organizes objects into groups that make numbers and addition easier to see.
Q17. Why are equal shares important?
Answer: Equal shares make fair groups or equal parts.
Q18. How do patterns help us predict?
Answer: A pattern rule tells us what should come next.
Q19. Why do we label a graph or table?
Answer: Labels tell us what the information represents.
Q20. How can you describe a shape?
Answer: Talk about its sides, corners, flat or curved surfaces, and other visible attributes.
Q21. How can you compare two objects?
Answer: Choose one attribute, such as length, mass, or capacity, and compare that same attribute.
Q22. Why is a calendar useful?
Answer: It organizes days, weeks, months, dates, and events.
Q23. Why does money have different values?
Answer: Different coins and bills represent different amounts of money.
Q24. Why should you explain your answer?
Answer: Explaining shows how you thought about the problem and helps you check your reasoning.
Q25. What should you do after a mistake?
Answer: Look at the step again, fix it, and try a similar example.
Q26. How can you be a confident math learner?
Answer: Use positive self-talk, try a strategy, ask questions, and remember that mistakes help you learn.
Q27. When should you use a picture?
Answer: Use a picture when it helps you see quantities, shapes, positions, or a story problem.
Q28. When should you use objects?
Answer: Use objects when you want to count, join, take away, share, sort, or compare in a hands-on way.
Q29. How can you check addition?
Answer: Recount the combined objects or use another model.
Q30. How can you check subtraction?
Answer: Put the taken-away part and the part left back together to see if they make the starting amount.