The average (arithmetic mean) of 10, 30, and 50 is 5 more than the average of 20, 40, and ?

Question: The average (arithmetic mean) of 10, 30, and 50 is 5 more than the average of 20, 40, and ?

Solution:
The average of 10, 30, and 50 is = (10 + 30 + 50)/3 = 30
The average of 20, 40 and x must be 30 - 5 = 25

ATQ,
(20 + 40 + x)/3 = 25
⇒ 60 + x = 75
∴ x = 15