The average (arithmetic mean) of 5,10,15 and x is 20 ... What is the x? How do I solve this question?

To find the mean (average), u add up all the numbers and divide by how many numbers there are.

(5 + 10 + 15 + x) / 4 = 20 ... simplify

(30 + x) / 4 = 20 ... multiply both sides by 4, eliminating the 4 on the left

30 + x = 20 * 4

30 + x = 80 ... subtract 30 from both sides

x = 80 - 30

x = 50

now lets check it ...

(5 + 10 + 15 + 50) / 4 = 20

80/4 = 20

20 = 20 (correct)

so ur answer is : x = 50 <===