Explaining Mathematical Reasoning · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Telling how you got your answer

Mathematics · Mathematical Thinking · ages 6-7
Name ______________________   Date ____________

  1. You do 9 plus 3 by making ten first. 9 plus 1 is 10, plus 2 more. What is the total?

    Answer: ______________

  2. Which of these explains how you solved 9 + 4, instead of just giving the answer?

    • I made ten first: 9 and 1 is 10, then 3 more is 13
    • I just knew it
    • 13 is a nice number

  3. If you check your answer a different way and get the same result, your first answer was probably right.

    Circle one:   True   False

  4. What can you use to show how you solved a problem?

    • Just the final answer
    • A drawing or number sentence
    • A guess

  5. Explain with cubes: 6 plus 7. Do 6 plus 6 is 12, plus 1 more. What is it?

    Answer: ______________

  6. Tom says 8 plus 4 equals 11. What is the error?

    • he doubled
    • he added 3 not 4
    • he added 5
    • he took away

  7. Ava checks 7 plus 5 equals 12 by doing 5 plus 7. She gets 12 again. She says the answer is correct. Is she right?

    Circle one:   True   False

  8. Show another way: 8 plus 5. Do 8 plus 2 is 10, plus 3. What is the total?

    Answer: ______________

  9. Zara says: 'I know 6 + 7 = 13, because 6 + 6 = 12, and 7 is one more than 6, so the answer is one more than 12.' Is this a good way to justify her answer?

    • No, doubles cannot be used this way
    • Yes, using a known double and adding one is a valid method
    • No, she must draw a picture instead

  10. Use ten first: 7 plus 9. 7 plus 3 is 10, plus 6. What is the total?

    Answer: ______________

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Answer key

For grown-ups. Fold this page away before handing over the rest.

Telling how you got your answer W1-mt_kJ5wYzO8qC-s1

  1. 12 · 9 plus 3 is 12.
  2. I made ten first: 9 and 1 is 10, then 3 more is 13 · Explaining your steps means telling how you got the answer, like making a ten first.
  3. True · Two different methods giving the same answer is good evidence that you are correct.
  4. A drawing or number sentence · A drawing or number sentence shows your thinking, not just the answer.
  5. 13 · Double 6 is 12, plus 1 is 13.
  6. he added 3 not 4 · 8 plus 4 is 12, so Tom is 1 short.
  7. True · Both orders give 12, so the check works.
  8. 13 · 8 plus 5 is 13.
  9. Yes, using a known double and adding one is a valid method · Starting from a known double and adjusting by one is a solid way to justify an answer.
  10. 16 · 7 plus 9 is 16.
Worksheet · LightMySky