a cistern is normally filled in 8 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 / 8 - 1 / x = 1 / 10 x = 40 answer : c"
inverse(subtract(divide(const_1, 8), divide(const_1, add(8, const_2))))