two pipes a and b can fill a tank in 30 hours and 45 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 / 30 part filled by b in 1 hour = 1 / 45 part filled by ( a + b ) in 1 hour = 1 / 30 + 1 / 45 = 5 / 90 = 1 / 18 both the pipes together fill the tank in 18 hours answer is a"
divide(const_1, add(divide(const_1, 30), divide(const_1, 45)))