Question

The sum of ages of father and son is 45 years. five years ago, the product of their ages was 4 times the father's sge at that time. the present age of father is

Answer 1

Let sons age = x years. Then fathers age = (45 - x)years. 
(x—5)(45—x—5) = 4(45- x - 5) hence (x—5) = 4 so x = 9 
Their ages are 36 years and 9 years.