The sum of the present age of a father and his son is 100 years. 5 years ago their age was in the ratio of 2 : 1. After 10 years the ratio of the age of father to that of his son will be?

5 : 3

⇒ Sum of present age = 100 yrs

⇒ 5 years ago the sum = 100 - 10 = 90years 

ATQ,

         F           S

Age   2     :     1 ⇒ 3R = 90 ⇒ 1R = 30

         ↓            ↓

      ×30       ×30

       60           30        (5 years ago)

     +15          +15  

       75            45        (after 10 years)

Ratio ⇒ 75 : 45 ⇒ 5 : 3