Using structure to calculate efficiently · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Using structure to calculate efficiently

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

  1. What is 34 + 10?

    304050+10
    • 35
    • 44
    • 24

  2. What's the fastest way to solve 4 + 8?

    • Count 4, then add 8 one by one
    • Flip it to 8 + 4 and count on from 8
    • Start over from 0

  3. A square and a rectangle both have 4 sides and 4 right angles.

    Circle one:   True   False

  4. What is 56 + 10?

    506070+10

    Answer: ______________

  5. You want to add 6 + 13 quickly. What should you do?

    • Count on from 6
    • Flip it to 13 + 6 and count on from 13
    • Multiply 6 and 13

  6. Which shape shares a square's pattern of having 4 sides and 4 right angles?

    • Triangle
    • Rectangle
    • Circle

  7. Ken is adding 7 + 15. He flips it to 15 + 7. Why does this still give the correct answer?

    • Because addition gives the same answer in any order
    • Because 15 is even
    • Because you always start with the smallest number

  8. Zara says 29 + 10 = 39 because only the tens digit changes. Ben says 29 + 10 = 20 because you just add a zero. Who is right?

    • Zara
    • Ben
    • Both
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Answer key

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

Using structure to calculate efficiently W1-mt_DW2D1c0fKx-s1

  1. 44 · Adding 10 only changes the tens digit. 3 tens becomes 4 tens, so 34 becomes 44.
  2. Flip it to 8 + 4 and count on from 8 · Starting from the bigger number, 8, means fewer counts to reach the answer.
  3. True · A square and a rectangle both have 4 sides and 4 right angles, even though their side lengths differ.
  4. 66 · Only the tens digit changes: 5 tens becomes 6 tens, so 56 becomes 66.
  5. Flip it to 13 + 6 and count on from 13 · Starting from 13 means only 6 more counts, instead of counting all the way from 6.
  6. Rectangle · A rectangle has 4 sides and 4 right angles too, just like a square.
  7. Because addition gives the same answer in any order · Addition gives the same answer no matter which order you add in, so flipping the numbers never changes the sum.
  8. Zara · 29 + 10 = 39. Only the tens digit changes, from 2 tens to 3 tens. The 9 ones stay the same.
Worksheet · LightMySky