Question

Three of four numbers have a sum of 22. If the average of the four numbers is 8, what is the fourth number ?

Answer 1

x+y+z=22

(x+y+z+t)/4=8
subsitute
x+y+z=22
(22+t)/4=8
multiplly by 4
22+t=32
subtract 22
t=10

the fourth number is 10