18 years ago, a man was three times as old as his son. Now, the man is twice as old as his son. The sum of the present ages of the man and his son is?
Note
Let the son's age 18 years ago be x years.
Then, man's age 18 years ago = 3x years.
(3x + 18) = 2 (x + 18)
⇒ 3x + 18 = 2x + 36
⇒ x = 18.
Sum of their present ages = (3x + 18 + x + 18) years
= (4x + 36) years
= (4 × 18 + 36) years
= 108 years.