The mean of four numbers is 30. if three of the numbers are 12, 50, and 48, what is the fourth number?

A. 120

B. 10

C. 12

D. 30

For example, n is the number we want to find

The sum of the four numbers divided by 4 is equal to the mean.

the sum/4 = mean

(12 + 50 + 48 + n) / 4 = 30

(110 + n) / 4 = 30

(110 + n) = 30 * 4

(110 + n) = 120

n = 120 - 110

n = 10

The fourth number is 10