Question

(05.02 MC)

Trevor solved the system of equations below. What mistake did he make in his work?

2x + y = 5
x − 2y = 10

y = 5 − 2x
x − 2(5 − 2x) = 10
x − 10 + 4x = 10
5x − 10 = 10
5x = 0
x = 0

2(0) + y = 5
y = 5

Answer 1

His work should have looked like this.

2x + y = 5
x − 2y = 10

y = 5 − 2x
x − 2(5 − 2x) = 10
x − 10 + 4x = 10
5x − 10 = 10                  When he added in both sides, he subtracted 10 from 10,
5x = 20                      instead of adding 10 from 10 to make 20.
x = 4
2(4) + y = 5
8 + y = 5

y = -3