(d) Let the time taken by pipe A = x min ∴ Time taken by pipe B = 3x min Now, by given condition, 3x - x = 20 ⇒ 2x = 20 ⇒ x =
20
2
=10 min ∴ Time taken by pipe A to fill the tank = 10 min. Time taken by pipe B to fill the tank = 3x min = 3 x 10= 30 min Now, time taken when both are open at same time to fill the tank =