Question

pipes A and B can fill a tank in 5 and 6 hours respectively. Pipe c can empty it in 12 hours. The tank is half full. All the three pipes are in operation simultaneously. After how much time will the tank will be full?

Answer 1

=1/5+1/6-1/12
=11/30-1/12
=(22-5)/60
=17/60
since tank is half full
then all three can fill it in 60/34 hours

Answer 2

A, B&C are in operation 1/5+1/6-1/12 =17/60 th part can be filled by three. The time required to complete the remaining part is 30/17 hourd