Find the error: subtraction across zeros

A find-the-error worksheet for regrouping through a zero, like 400 − 156 or 3,005 − 1,278. 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

Subtracted the smaller digit from the larger. Where the top digit was smaller, the student flipped the subtraction instead of regrouping.Example: 8,802 − 3,699 worked to 5,297 instead of 5,103.
Left the zero as 10 after regrouping through it. Regrouping through a 0 turns it into 10 and then gives 1 to the next place, so it ends as 9, not 10.Example: 500 − 285 worked to 225 instead of 215.

Grade 3 · 3.NBT.A.2, 4.NBT.B.4

Find the error: subtraction across zeros

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 8,802 − 3,699

Rosa's work

8802−36995297
1. Ones: 9 − 2 = 7.
2. Tens: 9 − 0 = 9.
3. Hundreds: 8 − 6 = 2.
4. Thousands: 8 − 3 = 5.
Rosa's answer: 5,297

Wrong step: What went wrong: Correct answer:
2 500 − 285

Ella's work

500−285225
1. Ones: 0 is less than 5 and the tens digit is 0. Regroup from the hundreds: 5 becomes 4, the tens digit becomes 10, and the ones become 10.
2. Ones: 10 − 5 = 5.
3. Tens: 10 − 8 = 2.
4. Hundreds: 4 − 2 = 2.
Ella's answer: 225

Wrong step: What went wrong: Correct answer:
3 700 − 353

Maya's work

700−353453
1. Ones: 3 − 0 = 3.
2. Tens: 5 − 0 = 5.
3. Hundreds: 7 − 3 = 4.
Maya's answer: 453

Wrong step: What went wrong: Correct answer:
4 303 − 265

Ravi's work

303−26548
1. Ones: 3 is less than 5 and the tens digit is 0. Regroup from the hundreds: 3 becomes 2, the tens digit becomes 10, and the ones become 13.
2. Ones: 13 − 5 = 8.
3. Tens: 10 − 6 = 4.
4. Hundreds: 2 − 2 = 0.
Ravi's answer: 48

Wrong step: What went wrong: Correct answer:

Free sheet from stepcheck.apps.clod.farm · every answer computed, not generated · sheet sample-subtraction-across-zeros

Answer key · Grade 3 · 3.NBT.A.2, 4.NBT.B.4

Find the error: subtraction across zeros

#	Wrong step	The mistake	Correct answer
1	Step 1	Subtracted the smaller digit from the larger. Where the top digit was smaller, the student flipped the subtraction instead of regrouping.Correct step 1: Ones: 2 is less than 9 and the tens digit is 0. Regroup from the hundreds: 8 becomes 7, the tens digit becomes 9, and the ones become 12.	5,103not 5,297
2	Step 1	Left the zero as 10 after regrouping through it. Regrouping through a 0 turns it into 10 and then gives 1 to the next place, so it ends as 9, not 10.Correct step 1: Ones: 0 is less than 5 and the tens digit is 0. Regroup from the hundreds: 5 becomes 4, the tens digit becomes 9, and the ones become 10.	215not 225
3	Step 1	Subtracted the smaller digit from the larger. Where the top digit was smaller, the student flipped the subtraction instead of regrouping.Correct step 1: Ones: 0 is less than 3 and the tens digit is 0. Regroup from the hundreds: 7 becomes 6, the tens digit becomes 9, and the ones become 10.	347not 453
4	Step 1	Left the zero as 10 after regrouping through it. Regrouping through a 0 turns it into 10 and then gives 1 to the next place, so it ends as 9, not 10.Correct step 1: Ones: 3 is less than 5 and the tens digit is 0. Regroup from the hundreds: 3 becomes 2, the tens digit becomes 9, and the ones become 13.	38not 48

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