Given: X is twice as old as Y Y is 5 times as old as Z Calculation: Let the age of X be x, Y be y and Z be z According to the question, x = 2y y = 5z ⇒ x = 10z According to the question, z + 5z + 10z = 64 ⇒ 16z = 64 ⇒ z = 4 years ∴ Age of Y = 5 × 4 = 20 years