RRB Group D 15-Oct-2018 Shift 1 Solved Paper

Question : 59 of 84

Marks: +1, -0

A cistern can be filled by one pipe in 12 hours and another in 15 hours. If both the pipes are left open at the same time, how long will it take for the cistern to be half full?

$6 {2}/{3}$ hours
$2 {1}/{3}$ hours
$4 {2}/{3}$ hours
$3 {1}/{3}$ hours

Validate

Solution:

One pipe filled a cistern in

1 {hr}={1}/{12}

\&

another pipe filled a cistern in

1 {hr}={1}/{15} {\hrs}

\∴

both pipe filled a cistern, when opens same time in

1 {hr}

={1}/{12}+{1}/{15}={5+4}/{60}

={9}/{60}={3}/{20}

\∴

Cistern should be half filled

={20}{3} \×{1}/{2}

={10}/{3} {hrs} \⇒3 {1}/{3} {hrs}

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