Question

If 8x−4y=20 and 4x−8y=4, what is the value of x−y?

(A) 1 (B) 2 (C) 3 (D) 4 (E) 6

Answer 1

Explanation:

Solve the system:

8x−4y=20

4x−8y=4

Reduce the first equation by dividing every term by -2:

-4x + 2y = -10

and then combine this result with the second equation:

4x−8y=4

-4x + 2y = -10

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-6y = -6, and so y = 1.

According to the first equation, if y = 1, then 4x - 8 = 4, or x = 3.

Then x = 3 and y = 1.

So, finally, x - y = 3 - 1 = 2