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➕ 3rd grade math · Add & Subtract

Estimate and check

An estimate is a quick answer that is close. Round each number to a friendly one, then do the math. 38.7 + 21.2: round to 40 + 21 = 61. The exact answer should be near 61. To check where the point goes in 6.8 × 3.1, think 7 × 3 = 21. So about 20, not 2 or 200.

Worked example

Round each number to the nearest whole number, then subtract to estimate 31.6 − 5.1.
Answer: 27
Round 31.6 to 32 and 5.1 to 5 (nearest whole number). Then 32 − 5 = 27.

For grown-ups: Estimate and check reasonableness. Below: three problems to try with the worked answers, and a free printable sheet. Children can practise the same skill as a game, with no sign-up and no ads.

  • CCSS 3.OA.D.8
What this practises, for teachers

Practices estimate and check reasonableness (3.OA.D.8). A printable sheet with its answer key, worked answers on the page, no accounts.

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For your class

🖨️ Printable sheet and key

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More printables, with answer keys, for this grade:

Try three

  1. Round each number to the nearest whole number, then subtract to estimate 30.6 − 4.5.
    Show the answer and how
    Answer: 26
    Round 30.6 to 31 and 4.5 to 5 (nearest whole number). Then 31 − 5 = 26.
  2. Round each number to the nearest whole number, then multiply to estimate 44.75 × 3.7.
    Show the answer and how
    Answer: 180
    Round 44.75 to 45 and 3.7 to 4 (nearest whole number). Then 45 × 4 = 180.
  3. Round each number to the nearest whole number, then multiply to estimate 54.3 × 5.69.
    Show the answer and how
    Answer: 324
    Round 54.3 to 54 and 5.69 to 6 (nearest whole number). Then 54 × 6 = 324.
Name: ____________________Date: ____________Score: ____ / 12

Estimate and check (3rd grade)

  1. Round each number to the nearest whole number, then add to estimate 21.5 + 7.7.
  2. Round each number to the nearest whole number, then add to estimate 14.1 + 14.4.
  3. Round each number to the nearest whole number, then add to estimate 28.7 + 19.4.
  4. Round each number to the nearest whole number, then subtract to estimate 25.74 − 16.93.
  5. Round each number to the nearest whole number, then add to estimate 6.51 + 33.6.
  6. Which is the best estimate of 239.158 ÷ 3.94?
  7. Round each number to the nearest whole number, then subtract to estimate 39.62 − 14.22.
  8. Round each number to the nearest whole number, then multiply to estimate 37.55 × 8.28.
  9. Which is the best estimate of 9.6 × 48.3?
  10. Which is the best estimate of 31.236 ÷ 1.37?
  11. Which is the best estimate of 80.96 ÷ 1.6?
  12. Which is the best estimate of 248.16 ÷ 9.4?

Answer key

  1. 30
  2. 28
  3. 48
  4. 9
  5. 41
  6. about 60
  7. 26
  8. 304
  9. about 500
  10. about 20
  11. about 50
  12. about 30

More 3rd grade skills: all 3rd grade math skills, or every grade at math skills.