Question

1. Two pipes A and B can separately fill a cistern in 12 and 15 mins respectively
while a third pipe C can empty it in 10 mins. How long will it take to fill the
cistern if all the pipes are opened simultaneously?
(B) 10
(C) 12
(D) 15
(A) 9​

Answer 1

Step-by-step explanation:

Part filled in 5 min =5×(

12

1

+

15

1

)

=5×

60

9

=

4

3

Part emptied in 1 minute when all the pipes are opened =

6

1

−(

12

1

+

15

1

)=

60

1

.

Now,

60

1

part is emptied in 1 minute.

Therefore,

4

3

part will be emptied in 60×

4

3

=45 minutes.