Math Drill Pages

Estimating Sums and Differences Worksheet

This 3rd grade sheet has 12 estimation problems with 3-digit numbers. Students round both numbers, write the rounded numbers, then add or subtract them. Part A rounds to the nearest 10 and Part B rounds to the nearest 100; each part has 3 sums and 3 differences, and every estimate is 1,000 or less.

Grade
Grade 3
Problems
12
Time
About 15 minutes
Standard
3.NBT.A.1
Download PDF (US Letter) Download PDF (A4)

Two pages: the worksheet, then the answer key. No sign-up needed.

Worksheet preview

Part A: Round to the nearest 10 Round each number to the nearest 10, then add or subtract.

  1. 636+123≈640+120=760
  2. 121+778≈120+780=900
  3. 869−198≈870−200=670
  4. 524+467≈520+470=990
  5. 832−256≈830−260=570
  6. 443−197≈440−200=240

Part B: Round to the nearest 100 Round each number to the nearest 100, then add or subtract.

  1. 725−414≈700−400=300
  2. 197+282≈200+300=500
  3. 696−462≈700−500=200
  4. 976−496≈1000−500=500
  5. 839+157≈800+200=1000
  6. 545+148≈500+100=600

Tips for teachers and parents

  • Round each number on its own first, then do the math with the rounded numbers. Writing the rounded numbers in the blanks keeps the two steps apart.
  • Rounding to estimate with tens gives a closer estimate; rounding to hundreds is quicker. Compare an answer from Part A with the exact answer to see how close it is.
  • After an estimate, ask: is the exact answer more or less than the estimate? For 443 − 197, the first number was rounded down and the second was rounded up, so the estimate of 240 is a little less than the exact difference.
  • Use estimates to check regrouping work: if 443 − 197 comes out as 354, the estimate of 240 shows something went wrong.

Common mistakes

  • Rounding the answer instead of the numbers, such as working out 443 − 197 = 246 and then rounding to 250. Estimation means rounding first, so the math is easy.
  • Mixing up places: rounding 696 to 690 in Part B, where the numbers are rounded to the nearest 100 (700).

What to practice next

Practice 3-digit addition and subtraction with regrouping, and estimate each answer first.

Frequently asked questions

How do you estimate a sum or difference by rounding?

Round each number to the same place, such as the nearest 10 or 100, then add or subtract the rounded numbers. 725 − 414 is about 700 − 400 = 300.

What grade learns estimation with rounding?

Grade 3. Common Core 3.NBT.A.1 covers rounding to the nearest 10 or 100, and 3.OA.D.8 asks students to use estimation to check whether an answer is reasonable.

Is there an answer key?

Yes, page 2 of the PDF shows the rounded numbers and the estimate for all 12 problems.