a cistern is normally filled in 10 hours but takes two hours longer to fill because of a leak in its bottom . if the cistern is full , the leak will empty it in ?
"1 / 10 - 1 / x = 1 / 12 x = 60 answer : c"
inverse(subtract(divide(const_1, 10), divide(const_1, add(10, const_2))))