Question

a father is 4 times as old as his son.after 5 years, he will be thrice his sons age.find there present ages.

Answer 1

Let the father's present age = x
              son's present age = y
as father is 4 times as old as his son,
   x = 4y   ---------------(1)

after 5 years,
 son's age = y+5
 father's age = x+ 5 

after 5 years, father's age will be thrice son's age.
x+5 = 3×(y+5)
⇒ 4y + 5 = 3y + 15
⇒ 4y - 3y = 15 - 5
⇒ y = 10 (son's present age)
   x = 4y = 10×4 = 40 (father's present age)