Find the error: multiplying decimals

A find-the-error worksheet for placing the decimal point in a product, like 2.4 × 1.3. 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.

Make this worksheet "Is it right?" version

Mistakes this sheet plants

Counted the decimal places of only one factor. The product has as many decimal places as both factors together: 1 + 1 = 2.Example: 9.5 × 0.3 worked to 28.5 instead of 2.85.
Multiplied the whole parts and the decimal parts separately. A decimal can't be split like that. Multiply as whole numbers, then place the decimal point.Example: 3.4 × 2.6 worked to 6.24 instead of 8.84.

Grade 5 · 5.NBT.B.7, 6.NS.B.3

Find the error: multiplying decimals

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 9.5 × 0.3

Ella's work
1. Multiply as whole numbers: 95 × 3 = 285.
2. 9.5 has 1 decimal place, so the product has 1.
3. The answer is 28.5.
Ella's answer: 28.5

Wrong step: What went wrong: Correct answer:
2 3.4 × 2.6

Ava's work
1. Multiply the whole numbers: 3 × 2 = 6.
2. Multiply the decimal parts: 4 × 6 = 24.
3. Put them together: 6.24.
Ava's answer: 6.24

Wrong step: What went wrong: Correct answer:
3 4.8 × 4.4

Rosa's work
1. Multiply the whole numbers: 4 × 4 = 16.
2. Multiply the decimal parts: 8 × 4 = 32.
3. Put them together: 16.32.
Rosa's answer: 16.32

Wrong step: What went wrong: Correct answer:
4 3.6 × 0.6

Ivy's work
1. Multiply as whole numbers: 36 × 6 = 216.
2. 3.6 has 1 decimal place, so the product has 1.
3. The answer is 21.6.
Ivy's answer: 21.6

Wrong step: What went wrong: Correct answer:

Free sheet from stepcheck.apps.clod.farm · every answer computed, not generated · sheet sample-multiplying-decimals

Answer key · Grade 5 · 5.NBT.B.7, 6.NS.B.3

Find the error: multiplying decimals

#	Wrong step	The mistake	Correct answer
1	Step 2	Counted the decimal places of only one factor. The product has as many decimal places as both factors together: 1 + 1 = 2.Correct step 2: 9.5 has 1 decimal place and 0.3 has 1, so the product has 2.	2.85not 28.5
2	Step 1	Multiplied the whole parts and the decimal parts separately. A decimal can't be split like that. Multiply as whole numbers, then place the decimal point.Correct step 1: Multiply as whole numbers: 34 × 26 = 884.	8.84not 6.24
3	Step 1	Multiplied the whole parts and the decimal parts separately. A decimal can't be split like that. Multiply as whole numbers, then place the decimal point.Correct step 1: Multiply as whole numbers: 48 × 44 = 2,112.	21.12not 16.32
4	Step 2	Counted the decimal places of only one factor. The product has as many decimal places as both factors together: 1 + 1 = 2.Correct step 2: 3.6 has 1 decimal place and 0.6 has 1, so the product has 2.	2.16not 21.6

stepcheck.apps.clod.farm · sheet sample-multiplying-decimals · the same link always prints this same sheet

A sample: open this exact sheet or make one with new numbers.