Question

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

He made no mistake

He subtracted 10 from the right side instead of adding 10 to the right side

He combined like terms incorrectly, it should have been 4x instead of 5x

He should have substituted 5 + 2x

Answer 1

The answer is He subtracted 10 from the right side instead of adding 10 to the right side

2x + y = 5
x - 2y = 10

y = 5 - 2x
x - 2(5 - 2x) = 10
x - 10 + 4x = 10
5x - 10 = 10

Here, he should add 10 to the right side:
5x = 10 + 10
5x = 20
x = 4
y = 5 - 2*4 = 5 - 8 = -3