Question

Two pipes A and B can fill a cistern in 37(1/2) minutes and 45 minutes respectively. Both pipes are opened. The cistern will be filled in just half an hour, if the B is turned off after:
A.5 min.
B.9 min.
C.10 min.
D.15 min.

Answer 1

the answer of this question is

9 minutes

Answer 2

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Pipe A can fill a tank in 371⁄2 minutes = 75⁄2 minutes

Pipe A can fill a tank in 371⁄2 minutes = 75⁄2 minutes=>Part filled by pipe A in 1 minute = 2⁄75

Pipe A can fill a tank in 371⁄2 minutes = 75⁄2 minutes=>Part filled by pipe A in 1 minute = 2⁄75 Pipe B can fill a tank in 45 minutes

Pipe A can fill a tank in 371⁄2 minutes = 75⁄2 minutes=>Part filled by pipe A in 1 minute = 2⁄75 Pipe B can fill a tank in 45 minutes=> Part filled by pipe B in 1 minute = 1⁄45

=> Part filled by Pipe A and B in 1 minute =

Assume that B is turned off after x minutes. i.e., for x minutes, both pipe A and B were open.

Part filled in x minutes by Pipe A and B =

x = 9