A man is five times as old as his son. four years later the sum of their ages will be 56 years. How old is the son at present?

Let the present age of man be x years and the age of his son be y years.
From 1st condition,
x = 5y .....(i)
From 2nd condition ,
(x + 4 ) + (y + 4) = 56
⇒ x + y + 8 = 56
⇒ x + y = 48 ... (ii)
Putting x = 5y in equation (ii)
5y + y = 48
⇒ 6y = 48
⇒ y = 8
∴ Age of son = 8 years