BPSC 60th-62nd Prelims Exam 12 Feb 2017 Solved Paper

Question : 59 of 150

Marks: +1, -0

In the bottom of a water tank, there are two drains A and B. If only A is open, it takes 30 minutes to empty a full tank and if only B is open, it takes 20 minutes. If for 10 minutes both drains are open, then B is closed, how much time it takes to empty a full tank ?

19 minutes
16 minutes
14 minutes
22 minutes
None of the above/More than one of the above

Validate

Solution:

Tank emptied by drain A in 1 minute

=\;{1}/{30}

Tank emptied by drain

{B}

in 1 minute

=\;{1}/{20}

∴

Tank emptied by drain A and B

=10(\;{1}/{30}+\;{1}/{20})=10(\;{2+3}/{60})

=10 × \;{5}/{60}=\;{5}/{6}

Remaining part

=1-\;{5}/{6}=\;{1}/{6}

Required time

=\;{1}/{6} × 30+10

=15

minute

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