Question

Two pipes A and B can fill a cestern in 3 hours and 5 hours respectively. if both the pipes are opened together. After how many hours, the tank would be full ?

Answer 1

Answer:

Lets check the rate at which they fill the cistern (fraction of cistern filled in an hour).

For A it is 1/3, for B it is 1/5 and for C it is -1/2 (since C does the reverse of what A and B do).

If all are open together the rates will add up:

1/3 + 1/5 - 1/2 = 8/15 - 1/2 = 1/30.

Since they fill 1/30th cistern in an hour, the cistern will be full in 30 hours.

Answer 2

Answer:

I think 30 hours but not so sure