Question
Two pipes A and B can fill a tank in 15 minutes and 20 minutes respectively . Both the pipes are opened together but after 4 minutes , pipe A is turned of . What is the total time required to fill he tank ?
Answer: Option D
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Part filled in 4 minutes = `4(1/15 + 1/20) = 7/15`
Remaining part = `(1 - 7/15) = 8/15`.
Part filled by B in 1 minute = `1/20`
`1/20 : 8/15 : : 1 : x or x = (8/15 xx 1 xx 20) = 10 2/3` min. = 10 min. 40 sec.
`:.` The tank will be full in (4 min. + 10 min.40 sec.) = 14 min. 40 sec.
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