Answer:
No mistake
Step-by-step explanation:
2x + y = 5
x - 2y = 10
y = 5 - 2x
x - 2(5 - 2x) = 10
x - 10 + 4x = 10
5x - 10 = 10
5x = 20
x = 4
2(4) + y = 5
y = -3
She made no mistake
You can check by plugging in x = 4 and y = -3 into the original equations . They fit exactly.