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Grade 2 · 2.NBT.B.5

Find the error: 2-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 69 + 19

Maya's work

69+1978
1. Add the ones: 9 + 9 = 18. Write 8.
2. Add the tens: 6 + 1 = 7.
Maya's answer: 78

Wrong step: What went wrong: Correct answer:
2 77 + 14

Ava's work

77+14811
1. Add the ones: 7 + 4 = 11. Write 11.
2. Add the tens: 7 + 1 = 8.
Ava's answer: 811

Wrong step: What went wrong: Correct answer:
3 56 + 16

Omar's work

56+16612
1. Add the ones: 6 + 6 = 12. Write 12.
2. Add the tens: 5 + 1 = 6.
Omar's answer: 612

Wrong step: What went wrong: Correct answer:
4 48 + 23

Jon's work

48+2361
1. Add the ones: 8 + 3 = 11. Write 1.
2. Add the tens: 4 + 2 = 6.
Jon's answer: 61

Wrong step: What went wrong: Correct answer:
5 48 + 15

Kai's work

48+15513
1. Add the ones: 8 + 5 = 13. Write 13.
2. Add the tens: 4 + 1 = 5.
Kai's answer: 513

Wrong step: What went wrong: Correct answer:
6 27 + 53

Sam's work

27+5370
1. Add the ones: 7 + 3 = 10. Write 0.
2. Add the tens: 2 + 5 = 7.
Sam's answer: 70

Wrong step: What went wrong: Correct answer:
7 48 + 32

Zoe's work

48+32710
1. Add the ones: 8 + 2 = 10. Write 10.
2. Add the tens: 4 + 3 = 7.
Zoe's answer: 710

Wrong step: What went wrong: Correct answer:
8 57 + 18

Jade's work

57+1865
1. Add the ones: 7 + 8 = 15. Write 5.
2. Add the tens: 5 + 1 = 6.
Jade's answer: 65

Wrong step: What went wrong: Correct answer:

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Answer key · Grade 2 · 2.NBT.B.5

Find the error: 2-digit addition with regrouping

#	Wrong step	The mistake	Correct answer
1	Step 1	Forgot to regroup. 9 + 9 = 18 makes a new ten, but the 1 ten was never added to the tens.Correct step 1: Add the ones: 9 + 9 = 18. Write 8, regroup 1 to the tens.	88not 78
2	Step 1	Wrote the whole ones sum. The ones make 11. Only the 1 goes in the ones place; the 1 ten is regrouped, not written next to it.Correct step 1: Add the ones: 7 + 4 = 11. Write 1, regroup 1 to the tens.	91not 811
3	Step 1	Wrote the whole ones sum. The ones make 12. Only the 2 goes in the ones place; the 1 ten is regrouped, not written next to it.Correct step 1: Add the ones: 6 + 6 = 12. Write 2, regroup 1 to the tens.	72not 612
4	Step 1	Forgot to regroup. 8 + 3 = 11 makes a new ten, but the 1 ten was never added to the tens.Correct step 1: Add the ones: 8 + 3 = 11. Write 1, regroup 1 to the tens.	71not 61
5	Step 1	Wrote the whole ones sum. The ones make 13. Only the 3 goes in the ones place; the 1 ten is regrouped, not written next to it.Correct step 1: Add the ones: 8 + 5 = 13. Write 3, regroup 1 to the tens.	63not 513
6	Step 1	Forgot to regroup. 7 + 3 = 10 makes a new ten, but the 1 ten was never added to the tens.Correct step 1: Add the ones: 7 + 3 = 10. Write 0, regroup 1 to the tens.	80not 70
7	Step 1	Wrote the whole ones sum. The ones make 10. Only the 0 goes in the ones place; the 1 ten is regrouped, not written next to it.Correct step 1: Add the ones: 8 + 2 = 10. Write 0, regroup 1 to the tens.	80not 710
8	Step 1	Forgot to regroup. 7 + 8 = 15 makes a new ten, but the 1 ten was never added to the tens.Correct step 1: Add the ones: 7 + 8 = 15. Write 5, regroup 1 to the tens.	75not 65

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