Question

pipes a and b can fill empty tank in 40 min and 60 min respectively and pipe c alone can empty full tank in x min.all three pipes are opened for 24min and then c is closed. a and b together full tank in another 16min.what is value of x?
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Answer 1

Pipe A can fill the tank in 40 min

so in one minute Pipe A fills 1/40th of the tank

Similarly Pipe B can fill 1/60th of the tank in one minute

So Pipes A and B together fill in one minute 1/40+1/60 of the tank

which is same as 5/120

Pipe C empties the tank say x min

Pipe C will empty 1/x of the tank in one minute

So in one minute (5/120 - 1/x) of the tank will be filled if Pipes A and B are filling along with Pipe C emptying.

This should be same as 1/30 because we want the tank to be full in 30 min

5/120 - 1/x = 1/30

rearranging

1/x = 5/120 - 1/30 =. 5/120. - 4/120 =1/120

Pipe C could empty the full tank in 120 min.

answer is 120 min

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