The average age of A and B is 18 years. After 3 years, C joins them and the average ages of A, B and C becomes 22 years. The age of C is

• 20 years

• 21 years

• 24 years

• 24 years

C.

24 years

Average age of A and B = 18 years
Total age of A and B = 18 x 2 = 36 years
Total age of A and B after 3 years  = 36 + 3 x 2 = 42 years
Total age of A, B and C = 3 x 22 = 66 years
∴  Age of C = 66 - 42 = 24 years.