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

a
He should have substituted 5 + 2x

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

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

d
He made no mistake

Answer 1

2x + y = 5

x − 2y = 10

y = 5 − 2x

x − 2(5 − 2x) = 10

x − 10 + 4x = 10

5x − 10 = 10

add 10 to each side

5x-10+10 = 10 + 10

5x=20

5x = 0 this is the error

He needs to add 10 to each side