5 years ago, the average age of P and Q was 15 years. Average age of P, Q and R today is 20 years. How old will R be after 10 years ?

Present age of (P + Q) = 30 + 10 = 40 years

(P + Q + R)’s present age = 20 × 3 = 60 years

R’s present age = 60 – 40 = 20 years

R’s age after 10 years = 20 + 10 = 30 years