Find the error: 3-digit addition with regrouping

A find-the-error worksheet for three-digit sums with one regroup, like 356 + 278. Each problem shows a student's worked solution with one planted mistake; students find the wrong step, name the misconception and solve it correctly. The answer key is computed, so it is always right.

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Mistakes this sheet plants

Forgot to regroup. A column added to 10 or more, but the regrouped 1 was not added to the next column.Example: 613 + 247 worked to 850 instead of 860.
Wrote the whole column sum. A column added to 10 or more and both digits were written down, instead of writing the ones digit and regrouping the 1.Example: 566 + 242 worked to 7,108 instead of 808.

Grade 3 · 3.NBT.A.2

Find the error: 3-digit addition with regrouping

Name Date

Each problem was solved by a student, and each has exactly one mistake. Find the step with the mistake, say what went wrong, and solve the problem correctly.

1 566 + 242

Kai's work

566+2427108
1. Add the ones: 6 + 2 = 8.
2. Add the tens: 6 + 4 = 10. Write 10.
3. Add the hundreds: 5 + 2 = 7.
Kai's answer: 7,108

Wrong step: What went wrong: Correct answer:
2 613 + 247

Tess's work

613+247850
1. Add the ones: 3 + 7 = 10. Write 0.
2. Add the tens: 1 + 4 = 5.
3. Add the hundreds: 6 + 2 = 8.
Tess's answer: 850

Wrong step: What went wrong: Correct answer:
3 129 + 464

Ella's work

129+4645813
1. Add the ones: 9 + 4 = 13. Write 13.
2. Add the tens: 2 + 6 = 8.
3. Add the hundreds: 1 + 4 = 5.
Ella's answer: 5,813

Wrong step: What went wrong: Correct answer:
4 441 + 160

Leo's work

441+160501
1. Add the ones: 1 + 0 = 1.
2. Add the tens: 4 + 6 = 10. Write 0.
3. Add the hundreds: 4 + 1 = 5.
Leo's answer: 501

Wrong step: What went wrong: Correct answer:

Free sheet from stepcheck.apps.clod.farm · every answer computed, not generated · sheet sample-three-digit-addition-regrouping

Answer key · Grade 3 · 3.NBT.A.2

Find the error: 3-digit addition with regrouping

#	Wrong step	The mistake	Correct answer
1	Step 2	Wrote the whole column sum. A column added to 10 or more and both digits were written down, instead of writing the ones digit and regrouping the 1.Correct step 2: Add the tens: 6 + 4 = 10. Write 0, regroup 1 to the hundreds.	808not 7,108
2	Step 1	Forgot to regroup. A column added to 10 or more, but the regrouped 1 was not added to the next column.Correct step 1: Add the ones: 3 + 7 = 10. Write 0, regroup 1 to the tens.	860not 850
3	Step 1	Wrote the whole column sum. A column added to 10 or more and both digits were written down, instead of writing the ones digit and regrouping the 1.Correct step 1: Add the ones: 9 + 4 = 13. Write 3, regroup 1 to the tens.	593not 5,813
4	Step 2	Forgot to regroup. A column added to 10 or more, but the regrouped 1 was not added to the next column.Correct step 2: Add the tens: 4 + 6 = 10. Write 0, regroup 1 to the hundreds.	601not 501

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