# In How Much Time Tank will be Filled. If A, B and C are Opened Successively for a Minute Each.

Two pipes A and B can separately fill a tank in 20minutes and 30minutes respectively while a third pipe C can empty it in 15 minutes. If A, B and C are opened successively for a minute each, the tank will be filled in

1. 60 minutes
2. 58 minutes
3. 172 minutes
4. 180 minutes
Monis Rasool Professor Asked on 10th November 2015 in

Answer is 172 minutes

Explanation:-
Pipe A can fill a tank = 20 minutes
Therefore, A can fill a tank in a minute = 1/20

Pipe B can fill a tank = 30 minutes
Therefore, B can fill a tank in a minute = 1/30

Pipe C can empty it = 15 minutes
Therefore, C can empty it in a minute = 1/15

A, B and C are opened = 1/20 + 1/30 – 1/15
= (3 + 2 – 4)/60
= 1/60

1/60 of a tank filled in 3 minutes,
Therefore,  [1 – (1/20 + 1/30)]
= 55/60
55/60 of a tank filled in 3 x 55 minutes
Now, 5/60 of the tank  remains to be filled.
A will fill 1/20  in 1 minute and B  will fill the remaining
= (5/60 – 1/20)
= 1/30 in 1 minute
Therefore, time required = 165 + 1 + 1 + 5
= 172 minutes

Hence, the answer is (3) 172 minutes.

Monis Rasool Professor Answered on 10th November 2015.