a cistern is filled by a tap in 3 1 / 2 hours . due to leak in the bottom of the cistern , it takes half an hour longer to fill the cistern . if the cistern is full how long will it take the leak to empty it ?
2 / 7 - 1 / x = 1 / 4 x = 28 answer : d
divide(const_1, subtract(divide(const_1, add(3, divide(1, 2))), divide(1, const_4)))