Average problem

[phoenix9801]

4-
The average (arithmetic mean) of 20, 60, and 100 is 10 more than the average of 40, 80, and which of the following?

A) 110
B) 90
C) 70
D) 50
E) 30

[aneesh.kg]

4-
The average (arithmetic mean) of 20, 60, and 100 is 10 more than the average of 40, 80, and which of the following?

A) 110
B) 90
C) 70
D) 50
E) 30

Let the unknown number be x. Then

(20 + 60 + 100)/3 = (40 + 80 + x)/3 + 10
60 = 40 + x/3 + 10
x = 30

[spoiler](E)[/spoiler] is correct.