Question

A tank can be filled by pipe A in 5 hours and by pipe B in 8 hours, each pump working on its own. When the tank is full and a drainage hole is open, the water is drained in 20 hours. If initially the tank was empty and someone started the two pumps together but left the drainage hole open, how long does it take for the tank to be filled

Answer 1

Explanation:

tank filled in 1 hour by pipe A=1/5

tank filled in 1 hour by pipe B=1/8

water drained out in 1 hour=1/20

tank filled in 1 hour by all three=1/5+1/8-1/20=(8+5-2)/40 =11/40 [L.C.M. of 5,8,20=40]

time taken to fill the tank=40/11=3 7/11 hours

Answer 2

The answer is 3.6 hours. that is how long it takes for the tank to be filled