Question

Analyzing an Error

A student simplifies (6b + 4r) – (2b + r) and says that the result is 4b + 5r. Explain the error and describe the correct steps to simplify the expression.

Answer 1

4b+3r

Explanation:

(6b+4r)-(2b+r)

Distribute the negative symbol across the second set of parenthesis.

6b+4r-2b-r

Add like terms

4b+3r

Error: the student added r instead of subtracting it. They most likely only distributed the negative to the 2b.

Answer 2

4b +3r

The student did not subtract both terms in the second parentheses

Explanation:

(6b + 4r) – (2b + r)

Distribute the minus sign to all terms in the second parentheses

6b + 4r – 2b - r

Combine like terms

6b -2b +4r -r

4b +3r

The student did not subtract both terms in the second parentheses