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NTSE Sample Paper NTSE SAT Practice Test-13

  • question_answer
    Three taps A, B and C can fill a tank in 12, 15 and 20 hours respectively. If A is open all  the time and B and C are open for one hour each alternately, the tank will be full in

    A) 6 hrs                            

    B) 62 hrs

    C) 7 hrs         

    D) \[7\frac{1}{2}\]hrs.

    Correct Answer: C

    Solution :

    [c](A+B)'s  1 hour work \[=\left( \frac{1}{12}+\frac{1}{15} \right)=\frac{3}{20}\] (A+ C)'s 1 hour work \[=\left( \frac{1}{12}+\frac{1}{20} \right)=\frac{2}{15}\] Part filled in 2 hours \[=\frac{3}{20}+\frac{2}{15}=\frac{17}{60}\] \[\therefore \] Part filled in 6 hours \[=3\times \frac{17}{60}=\frac{17}{20}\] Remaing part to be filled \[=1-\frac{17}{20}=\frac{3}{20}\] This is now filled by (A + B) in 7th hour. Total time = 7 hours.                   


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