Pipes and Cisterns Practice Test 1 with solutions

Question : 35 of 40

Marks: +1, -0

Three taps A, B and C can fill a tank in 12, 15 and 20 hours respectively. If A is opened all the time and B and C are opened for one hour each alternately, the tank will be full in

5 hrs.
6 hrs.
$6 2/3$ hrs.
7 hrs.

Validate

Solution:

In 1 hour the part filled by (A + B) =

1/{12}+1/{15}

3/{20}

In 1 hour the part filled by (A + C) =

1/{12}+1/{20}

2/{15}

Hence, in 2 hours the part filled by (A + B + C) =

3/{20}+2/{15}

{17}/{60}

Then, in 6 hours the part filled by (A + B + C) = 3 ×

{17}/{60}

{17}/{20}

Remaining part = 1 –

{17}/{20}

3/{20}

, which is filled by (A + B) in 1 hour.
Hence, total time taken = 6 + 1 = 7 hours.

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