If 2x + y = 7 and y + 2z = 23, what is the average of x, y, and z?

If 2x + y = 7 and y + 2z = 23, what is the average of x, y, and z?

A. 5
B. 7.5
C. 15
D. 12.25

Add both equations to get all variables together:
2x + y + y + 2z = 23 + 7
2x + 2y + 2z = 30

We can divide both sides by 2 to simplify:
(2x + 2y + 2z)/2= 30/2
x + y + z = 15

Notice: the average of x, y, and z is:
(x + y + z)/3

But x + y + z = 15, so we have:
15/3 = 5, answer A