Given: The ratio between the present age of father and mother is 10 ∶ 9 The ratio between the present age of the father and his son is 5 ∶ 2 Concept: Ratio and proportion Calculation: Let be assume the age of the father and his son is 5x and 2x respectively. Difference of age of father and his son 4 year ago = (5x - 4) - (2x - 4) = 30, x = 10 Present age of father = 5 × 10 = 50 year, Present age of his son = 2 × 10 = 20 years The present age of mother =9×(
50
10
)=45 years Sum of there age = 50 + 45 + 20 = 115 ∴ The required result will be 115.