The total of the ages of A, B ahd C at present is 90 years. Ten years ago, the ratio of their ages was 1: 2: 3. What is the age of B at present?

A. 40
B. 20
C. 30
D. 18
Answer: C

Explanation:  

Let their ages 10 years ago is x, 2x and 3x years.
(x + 10) + (2x + 10) + (3x + 10) = 90 hence x= 10
B’s present age = (2x + 10) =30 years.