Estimating by rounding · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Estimate First, Then Check Your Work

Mathematics · Addition & Subtraction · ages 7-9
Name ______________________   Date ____________

  1. Round 42 to the nearest 10.

    4041424344454647484950rounds down
    • 40
    • 50
    • 42

  2. You can check 50 - 20 = 30 by adding 30 + 20 to see if you get 50.

    Circle one:   True   False

  3. What is a good estimate for 39 + 21?

    • 50
    • 60
    • 70

  4. Tia wants to estimate 48 + 31. Round each number to the nearest ten, then add. What is the estimate?

    • 70
    • 80
    • 90
    • 100

  5. Ben says 46 + 37 = 103. Round each number to the nearest ten and add. Is 103 a reasonable answer?

    Circle one:   True   False

  6. Estimate 236 + 158 by rounding each number to the nearest hundred. What is the estimate?

    Answer: ______________

  7. Tom adds 154 + 238 and gets 392. Check his answer with subtraction: 392 - 238 = ?

    Answer: ______________

  8. Estimate 312 - 96 by rounding each number to the nearest hundred. What is the estimate?

    Answer: ______________

  9. Lily subtracts 502 - 248 and gets 254. Which calculation checks whether her answer is correct?

    • 502 + 248 = 254
    • 254 - 248 = 502
    • 254 + 248 = 502

  10. Priya estimates 495 + 512 as about 1000. She calculates the exact answer and gets 107. What is most likely wrong?

    • Her estimate was wrong
    • She made a mistake in her exact calculation
    • 495 and 512 did not need estimating
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Answer key

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

Estimate First, Then Check Your Work W1-mt_QaYfeVL-0C-s1

  1. 40 · 42 is closer to 40 than to 50, so it rounds down to 40.
  2. True · Addition undoes subtraction, so 30 + 20 should equal 50, and it does.
  3. 60 · Round 39 to 40 and 21 to 20, then add: 40 + 20 = 60.
  4. 80 · 48 rounds to 50 and 31 rounds to 30. 50 + 30 = 80, so 80 is a good estimate.
  5. False · The estimate is 50 + 40 = 90. 103 is much bigger than 90, so the answer is not reasonable and Ben should check his work.
  6. 400 · 236 rounds to 200 and 158 rounds to 200. 200 + 200 = 400.
  7. 154 · If 154 + 238 = 392, then 392 - 238 should bring you back to 154, and it does.
  8. 200 · 312 rounds to 300 and 96 rounds to 100. 300 - 100 = 200.
  9. 254 + 248 = 502 · If the subtraction is right, adding the answer back to the number subtracted should return the original number: 254 + 248 = 502.
  10. She made a mistake in her exact calculation · 107 is nowhere near the estimate of 1000, so the exact calculation has an error, not the estimate.
Worksheet · LightMySky