Question
Two pipes A and B can fill a cistern in `37 1/2` minutes and 45 minutes respectively . Both pipes are opened . he cistern will be filled in just half an hour , if the pipe B is turned off after :
Answer: Option B
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Let B be turned off after `x` minutes . Then
Part filled by (A + B) in `x` min. + part filled by A in (30 - `x`) min. = 1.
`:.` `x(2/75 + 1/45) + (30 - x). 2/75` = 1
`hArr (11x)/(225) + ((60 - 2x))/(75) = 1 hArr 11x + 180 - 6x = 225 hArr x = 9`
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