a cistern can be filled by a tap in 3 hours while it can be emptied by another tap in 9 hours . if both the taps are opened simultaneously , then after how much time will the cistern get filled ?
"net part filled in 1 hour = 1 / 3 - 1 / 9 = 2 / 9 therefore the cistern will be filled in 9 / 2 hours or 4.5 hours . answer : a"
divide(const_1, subtract(divide(const_1, 3), divide(const_1, 9)))