Question 1 (Multiple Choice Worth 4 points)
[6.02] Carlos 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
He should have substituted 5 + 2x
He...