Roberts father is 4 times as old as Robert. After 5 years, father will be three times as old as Robert. Find their present ages.

Let Robert's age is 'x'

Robert's Father's age is four times as old as Robert = 4x

In five years time, Robert's age is = x + 5

and Robert's Father's age is = 4x + 5

In five years time:

Robert's Father's age = 3 * Robert's age

4x + 5 = 3 (x+5)

4x + 5 = 3x + 15

4x - 3x = 15 - 5

x = 5

Robert's present age = 5

Robert's Father's age = 4 * 5 = 20