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

Let the unknown number be x.
as the average of the four numbers is 8
⇒ (22 + x)/4 = 8
⇒22 + x = 32
⇒x = 10

Answer 2

The 4th number is 10, since you need to add 10 to get 32 so that when you divide by 4 you get 8