8th grade math question?

Question

The mean of these six numbers is 20.38. What is the missing number?

25.14, 17.22, 23.04, 20.21 21.27, ___

To what sets of numbers does the number -8 belong?

Answer 1

mean is sum/n

n=6

sum= 25.14+....the others, + x, which is the missing number

so when you take the (sum+x)/6=20.38, you can solve for x.

multiply both sides by 6, subtract both sides by sum, and you get x, the missing number

(106.88+x)/6=20.38

x=15.4

Answer 2

15.4 is correct.

Answer 3

15.4

Answer 4

23.20