Father is five times as old as his son. After 2 years, the father will be four times as old as his son. What is the present age of the father ? 

Let the age of son = x yrs.

So, the age of the father will be 5x.

Given condition: After two years, father’s age = 4 times of son's age
5x + 2 = 4 ( x + 2)
5x + 2 = 4 x + 8
5x − 4x = 8 − 2
x = 6
Hence son’s present age = 6 years;
and father’s present age = 5 x = 5 × 6 = 30 years