If the AVERAGE of x and y is 5, just make both of them 5. Or better yet, their sum is 10.

If the average of x, y, and z is 8, that means the sum of x,y, & z is 24.

24 – 10 = 14.

(x+y) / 2 = 5

(x+y+z) / 3 = 8

do process of elimination

or just think about it…its not that hard, z = 14

because x+y=10 (because you divide the answer by 2 and get 5)

so x+y+z = 10 + z, and the answer needs to be 24 (because 24 / 3 is the only way to get the answer 8)

so 10 + [what number] = 24

10+14 = 24

therefore z=24

(x + y + z)/3 = 8

x + y = 10

x + y + z = 24

but we know that x + y = 10, so we can write

10 + z = 24,

therefore z = 14

(10+z)/3=8……….10+z=24

z=14