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Subtract by adding on: 1st grade math

Subtraction as an unknown addend. A free 1st grade lesson plan, a question set with answers and a printable sheet with its key. Copy it and make it yours.

Lesson plan

Goal

  • Students can do this: subtraction as an unknown addend.

Teach (10 min)

  • 3, 5 and 8 make 3 + 5 = 8, 5 + 3 = 8, 8 − 3 = 5, 8 − 5 = 3.
  • If you know one fact, you know the family.
  • Work one example on the board while students say each step aloud, then do one together.

Practise (15 min)

  • Students work the printable sheet in pairs, then alone.
  • Or practise it as a game with no sign-up: https://peabody.kids/math/numsense.g1_family?lesson=1-numsense-family-1&at=1

Exit ticket (5 min)

  • Three questions on a slip:
  • 1. Look at this fact: 4 + 6 = 10. Which fact is in the same fact family? (It uses the same three numbers: 4, 6, 10.)
  • 2. These facts use the same three numbers (6, 8, 14): 8 + 6 = 14, 6 + 8 = 14, and 14 − 8 = 6. Find the missing number in the last fact: 14 − 6 = ?
  • 3. Look at this fact: 9 − 6 = 3. Which fact is in the same fact family? (It uses the same three numbers: 3, 6, 9.)

Question set

10 questions that read in words, easiest first. Questions that need a picture are on the printable sheet below.

  1. Look at this fact: 4 + 6 = 10. Which fact is in the same fact family? (It uses the same three numbers: 4, 6, 10.)
  2. These facts use the same three numbers (6, 8, 14): 8 + 6 = 14, 6 + 8 = 14, and 14 − 8 = 6. Find the missing number in the last fact: 14 − 6 = ?
  3. Look at this fact: 9 − 6 = 3. Which fact is in the same fact family? (It uses the same three numbers: 3, 6, 9.)
  4. These facts use the same three numbers (2, 6, 8): 2 + 6 = 8, 6 + 2 = 8, and 8 − 2 = 6. Find the missing number in the last fact: 8 − 6 = ?
  5. These facts use the same three numbers (2, 3, 5): 2 + 3 = 5, 3 + 2 = 5, and 5 − 2 = 3. Find the missing number in the last fact: 5 − 3 = ?
  6. Look at this fact: 11 − 6 = 5. Which fact is in the same fact family? (It uses the same three numbers: 5, 6, 11.)
  7. Look at this fact: 8 + 7 = 15. Which fact is in the same fact family? (It uses the same three numbers: 7, 8, 15.)
  8. Look at this fact: 3 + 4 = 7. Which fact is in the same fact family? (It uses the same three numbers: 3, 4, 7.)
  9. These facts use the same three numbers (1, 7, 8): 7 + 1 = 8, 1 + 7 = 8, and 8 − 7 = 1. Find the missing number in the last fact: 8 − 1 = ?
  10. These facts use the same three numbers (4, 8, 12): 8 + 4 = 12, 4 + 8 = 12, and 12 − 8 = 4. Find the missing number in the last fact: 12 − 4 = ?
Answers
  1. 10 − 6 = 4
  2. 8
  3. 9 − 3 = 6
  4. 2
  5. 2
  6. 11 − 5 = 6
  7. 15 − 8 = 7
  8. 7 − 3 = 4
  9. 7
  10. 8

Printable sheet

Name: ____________________   Date: ____________

Subtract by adding on (1st grade)

  1. These facts use the same three numbers (4, 8, 12): 8 + 4 = 12, 4 + 8 = 12, and 12 − 8 = 4. Find the missing number in the last fact: 12 − 4 = ?
  2. Look at this fact: 4 + 8 = 12. Which fact is in the same fact family? (It uses the same three numbers: 4, 8, 12.)
  3. Look at this fact: 7 − 2 = 5. Which fact is in the same fact family? (It uses the same three numbers: 2, 5, 7.)
  4. These facts use the same three numbers (1, 8, 9): 8 + 1 = 9, 1 + 8 = 9, and 9 − 8 = 1. Find the missing number in the last fact: 9 − 1 = ?
  5. These facts use the same three numbers (1, 5, 6): 5 + 1 = 6, 1 + 5 = 6, and 6 − 5 = 1. Find the missing number in the last fact: 6 − 1 = ?
  6. Look at this fact: 9 − 3 = 6. Which fact is in the same fact family? (It uses the same three numbers: 3, 6, 9.)
  7. Look at this fact: 6 + 3 = 9. Which fact is in the same fact family? (It uses the same three numbers: 3, 6, 9.)
  8. Look at this fact: 10 + 11 = 21. Which fact is in the same fact family? (It uses the same three numbers: 10, 11, 21.)
  9. Look at this fact: 4 + 9 = 13. Which fact is in the same fact family? (It uses the same three numbers: 4, 9, 13.)
  10. Look at this fact: 12 − 10 = 2. Which fact is in the same fact family? (It uses the same three numbers: 2, 10, 12.)
  11. Look at this fact: 10 + 5 = 15. Which fact is in the same fact family? (It uses the same three numbers: 5, 10, 15.)
  12. Look at this fact: 7 + 12 = 19. Which fact is in the same fact family? (It uses the same three numbers: 7, 12, 19.)
Key
  1. 8
  2. 12 − 8 = 4
  3. 7 − 5 = 2
  4. 8
  5. 5
  6. 6 + 3 = 9
  7. 9 − 3 = 6
  8. 21 − 10 = 11
  9. 13 − 4 = 9
  10. 2 + 10 = 12
  11. 15 − 5 = 10
  12. 19 − 12 = 7

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