Practice Test Discussion


A tank can be filled by a pipe A in 2 h and pipe B in 6 h. At 10 am pipe A was opened. At what time will the tank be filled if pipe B is opened at 11 am?

 [SSC CGL 2012]

  • Explanation

    According to the question,

    Pipe A fills the tank in 2 hours (in 1 hour it fills 12 part of the tank)

    Pipe B fills the tank in 6 hours (in 1 hour it fills 16 part of the tank)

    As pipe A was opened at 10:00 am and it worked alone till 11:00 am. In 1 hour it will fill 12 part of the tank.

    the remaining 12 part of the tank will be filled by both Pipe A and B. 

    According to the formula, if pipe A can comletely fill a tank in x hours and pipe B can comletely fill a tank in y hours, then the time taken by both pipes together to fill the tank is xyx+y hours.

    So, 2×62+6=128=32 part (both the pipes together will fill 32 part of the tank)

    So, Time taken by both pipes to fill 32 part of the tank = 60 minutes
    Time taken to fill 12 part = 60×32×12 = 45 minutes

    Therefore, the tank will be filled at 11:45 AM

    Hence option C is correct.

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    Pipes and cisterns

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