Question

Juanita ran 8.3 miles in Week 1 and 12.09 miles in Week 2. She used the subtraction below to determine how much farther she ran in Week 2 than in Week 1.

12.09 minus 8.30 = 4.79. All decimals are aligned. The 0 in 12.09 is crossed out and a 1 is above it. The 2 is crossed out in 12.09 and a 1 is above it.

Which error did Juanita make?
She subtracted instead of added.
She aligned the decimal points incorrectly.
She did not regroup correctly when subtracting.
She made a computational error when subtracting.

Answer 1

Explanation:

12.09 - 8.30 = 3.79

The reason why her answer was wrong is because when the '2' gets slashed into a '1' during carry over, it would have been 11 - 8 = 3 instead of a 4. (the 1st column)

The error that Juanita made is that she made a computational error when subtracting.

Answer 2

• She made a computational error when subtracting.

Explanation:

She subtracted instead of added.

• No, she needed to subtract to find the difference.

She aligned the decimal points incorrectly.

• No, she did it right.

She did not regroup correctly when subtracting.

• No, she regrouped correctly.

She made a computational error when subtracting.

• Yes. She made an error at last step, instead of subtracting 8 from 11 she subtracted 8 from 12 and got the first digit wrong (4 instead of 3).