Given: Ratio of present age of sisters = 5 ∶ 7 ∶ 11 Present age of mother = 45 years Difference between age of elder sister and mother = 23 years Concept: Calculate the present age of elder sister, then equate with the rest of the ratios to find the present age of youngest sister. Calculation: Let the present ages of the 3 sisters = 5x, 7x, 11x Present age of elder sister = 45 – 23 = 22 years ∵ The present age of elder sister = 11x = 22 years ∴ 11x = 22 ⇒ x = 22/11 ⇒ x = 2 ∴ Present age of youngest sister = 5 × 2 = 10 years ⇒ Her age after 10 years from now = 10 + 10 = 20 years