two pipes a and b can fill a tank in 18 hours and 24 hours respectively . if both the pipes are opened simultaneously , how much time will be taken to fill the tank ?
"part filled by a in 1 hour = 1 / 18 part filled by b in 1 hour = 1 / 24 part filled by ( a + b ) in 1 hour = 1 / 18 + 1 / 24 = 7 / 72 both the pipes together fill the tank in 72 / 7 = 10 2 / 7 hours answer is d"
divide(const_1, add(divide(const_1, 18), divide(const_1, 24)))