A cistern has two inlets A and B which can fill it in 12 minutes and 15 minutes respectively. An outlet C can empty the full cistern in 10 minutes. If all the three pipes are opened together in the empty tank, how much time will they take to fill the tank completely?

Question

Philoid · Accepted Answer

Number of hours inlet A requires to fill the cistern : 12 min = = hours

Number of hours inlet B requires to fill the cistern : 15 min = = hours

Number of hours outlet C requires to empty the cistern : 10 min = = hours

Part of the cistern filled by inlet A in one hour: 5

Part of the cistern filled by inlet B in one hour: 4

Part of the cistern emptied by outlet C in one hour: 6

Work done by pipes A, B and C together in one hour: 5 + 4 – 6 = 3

They can fill the cistern together in hours = 20 min