There are three pipes A B and C attached to container A and B can fill the container alone in 20 and...........

Quantitative Aptitude ( CCS) Pipes&cistern

There are three pipes, A, B and C, attached to container. A and B can fill the container alone in 20 and 30 mins, respectively whereas C can empty the container alone in 45 mins. The three pipes are kept opened alone for one minute each in the the order A, B and C. The same order is followed subsequently. In how many minutes will the reservoir be full?

25 min

35 min

20 min

47 min

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Explanation:

Solution:
A……20 9unit (180/20)
B……30 180 (LCM) 6unit
C……45 4unit
1st Minute => A is opened => fills 9 L
2nd Minute => B is opened =>fills another 6 L
3rd Minute => C is opened => empties 4 L
Hence every 3 minutes => (9 + 6 – 4 =) 11 litres are filled into the container.
So in 45 minutes (11 × 15 =) 165 litres are filled.
In the 46th minute A is opened and it fills 9 litres. In the 47th minute B is opened and it fills 6 litres.
Hence the container will be full in 47 minutes.