Solution:Let the 3 persons be A, B and C.
Given: The ratio of the present ages of 3 persons is 4 : 7 : 9
Let the present age of A, B and C be 4x, 7x and 9x years respectively.
A : B : C ⇒ 4x : 7x : 9x
Given, 8 years ago, the sum of their ages was 56.
8 years ago, the ratio of the ages is
A : B : C ⇒ 4x − 8 : 7x − 8 : 9x − 8
Given, the sum of the above ages was 56.
4x − 8 + 7x − 8 + 9x − 8 = 56
⇒ 20x − 24 = 56
⇒ 20x = 56 + 24
⇒ 20x = 80
⇒ x = 4
So, present ages of A, B and C be 4 × 4, 7 × 4, 9 × 4
i.e. 16, 28 and 36 respectively.