Given 1st tap can empty the tank in 30 minutes. ∴ In 1 min, it can empty 1/ 30th part of tank 2nd can empty the tank in 45 min ∴ In 1 min it can empty 1/ 45th part of the tank Working together, in 1 min they can empty volume of tank = 1/30 + 1/45 ⇒ Working together in 1 min they can empty volume of tank = 5/90 = 1/18 of the tank volume ∴ To empty the whole tank, time taken = 18 min