Question

Two pipes A and B can fill an empty tank in 3hrs and 5hrs respectively. Pipe C can empty the full tank in 6 hours. If the three pipes A, B, and Care opened at the same time, find how long it will take for the tank to be full. *​

Answer 1

30/11

Explanation:

Imagine the tank can hold x litre of water

So,A can fill x/3 litre water per hour

And B can fill x/5 litre water per hour

And C can reduce x/6 litre of water per hour which is filled by A and B.

So the gross calculation per hour is:

(x/3+x/5)-x/6

=11x/30

Now suppose it tooks 'a' hour to fill the tank.

So, a(11x/30)=x

⇨ a= (30/11x)x

⇨a=30/11

Answer 2

30/11 (hours)

Explanation:

Pipe A can fill the tank until it is full in 3 hours.

=> In 1 hour, pipe A can fill 1/3 of tank

Pipe B can fill the tank until it is full in 5 hours.

=> In 1 hour, pipe A can fill 1/5 of tank

Pipe C can empty the full tank in 6 hours.

=> In 1 hour, pipe A can empty 1/6 of tank

Assume that we open 3 pipes A, B, and C at the same time.

Then, in 1 hour, the amount of water in tank is:

A = 1/3 + 1/5 - 1/6 = 10/30 + 6/30 - 5/30 = 11/30 (tank)

=> The time to fill up the tank is:

T = 1/A = 1/(11/30) = 30/11 (hours)