If x+y=8z, then which of the following represents the average (arithmetic mean) of x, y, and z, in terms of z?
Pick any number like X=12, Y=4 and Z= 2 so that X+Y=8Z, now then the arithmetic mean will be (12+4+2)/3=6. Now, just look at the answers and put the value of Z there.
(A) 2.2+1=5, but it should be 6.
(B) 3.2=6, it can be the answer, lets check us the other options
(C) 5.2=10, no
(D) 2/3, no
(E) (3.2)/2=3, no
so the answer will be B..