Find the error: adding and subtracting integers

A find-the-error worksheet for negative numbers: −5 − (−8), −9 + 4, 3 + (−7). 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 a negative as if it were positive. Subtracting −4 is the same as adding 4.Example: −6 − (−4) worked to −10 instead of −2.
Added the sizes when the signs are different. With different signs, subtract the smaller size from the larger and keep the sign of the larger size.Example: −7 + 1 worked to −8 instead of −6.
Kept the sign of the first number. With different signs, the answer takes the sign of the number with the larger size, not the first number.Example: 9 + (−10) worked to 1 instead of −1.

Grade 7 · 7.NS.A.1

Find the error: adding and subtracting integers

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 −6 − (−4)

Zoe's work
1. Subtract 4: −6 − 4.
2. −6 − 4 = −10.
Zoe's answer: −10

Wrong step: What went wrong: Correct answer:
2 −7 + 1

Tess's work
1. The signs are different. Add the sizes: 7 + 1 = 8.
2. Keep the sign of −7: −8.
Tess's answer: −8

Wrong step: What went wrong: Correct answer:
3 9 + (−10)

Kai's work
1. The signs are different. Subtract the sizes: 10 − 9 = 1.
2. Use the sign of the first number, 9: 1.
Kai's answer: 1

Wrong step: What went wrong: Correct answer:
4 −13 − (−2)

Ben's work
1. Subtract 2: −13 − 2.
2. −13 − 2 = −15.
Ben's answer: −15

Wrong step: What went wrong: Correct answer:

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

Answer key · Grade 7 · 7.NS.A.1

Find the error: adding and subtracting integers

#	Wrong step	The mistake	Correct answer
1	Step 1	Subtracted a negative as if it were positive. Subtracting −4 is the same as adding 4.Correct step 1: Subtracting −4 is the same as adding 4: −6 + 4.	−2not −10
2	Step 1	Added the sizes when the signs are different. With different signs, subtract the smaller size from the larger and keep the sign of the larger size.Correct step 1: The signs are different. Subtract the sizes: 7 − 1 = 6.	−6not −8
3	Step 2	Kept the sign of the first number. With different signs, the answer takes the sign of the number with the larger size, not the first number.Correct step 2: Use the sign of the larger size, −10: −1.	−1not 1
4	Step 1	Subtracted a negative as if it were positive. Subtracting −2 is the same as adding 2.Correct step 1: Subtracting −2 is the same as adding 2: −13 + 2.	−11not −15

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