Two pipes can fill a tank in 15 hours and 4 hours respectively , while a third pipe can emplty it in 12 hours, How long ( in hours) will it take to fill the empty tank if all the three pipes are opened simultaneously ?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e.
The first pipe can fill the tank = 15 hours
The second pipe can fill the tank = 4 hours
The third pipe can empty the tank = - 12 hours
Capacity of the tank = LCM of 15, 4, and 12 = 60
Efficiency of the first tank = 4
Second tank = 15
Third tank = - 5
Combined efficiency of all three pipes = 4 + 15 - 5 = 14
Total time = 60/14 = 30/7 hours