Question

Becky and Tommy are asked to solve −4x − 25 = 8x + 15. Identify where one of them made an error.

Becky
−4x − 25 = 8x + 15
−4x − 25 − 8x = 8x + 15 − 8x
−12x − 25 = 15
-12x − 25 + 25 = 15 + 25
−12x = 40
Negative 12x over 40 equals 40 over 40
x equals negative three-tenths.

Tommy
−4x − 25 = 8x + 15
−4x − 25 + 4x = 8x + 15 + 4x
−25 = 12x + 15
−25 − 15 = 12x + 15 − 15
−40 = 12x
negative 40 over 12 equals 12x over 12
x equals negative ten-thirds

Becky made the error when she subtracted 8x

Becky made the error when she divided by 40

Tommy made the error when he added 4x

Answer 1

Tommy made the error when he added 15

Answer 2

Becky made the error when she divided by 40