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    A tank can be filled by two taps A and B in 8 hours and 10 hours, respectively. The full tank can be emptied by a third tap in 12 hours. If all the ta
    Question

    A tank can be filled by two taps A and B in 8 hours and 10 hours, respectively. The full tank can be emptied by a third tap in 12 hours. If all the taps are turned on at the same time, in how much time (in approximate number of hours) will the empty tank be filled completely?

    A.

    7

    B.

    8

    C.

    10

    D.

    9

    Correct option is A

    Given:
    Tap A fill the tank in 8 hours
    Tap B fill the tank in 10 hours
    Tap C empty the tank in 12 hours
    Formula Used:
    Time=WorkEfficiency\text{Time} = \frac{\text{Work}}{\text{Efficiency}}​​
    Solution:
    LCM of 8, 10, 12 = 120
    Total capacity of tank = 120 units
    Efficiency of Tap A = 1208\frac{120}{8}​ = 15 units

    Efficiency of Tap B =12010\frac{120}{10}​ = 12 units

    Efficiency of Tap C = 12012\frac{120}{12}​ = 10 units
    Effective of these three tanks together = (15 + 12 – 10) = 17 unit
    Time taken to fill the tank when they all opened simultaneously = 12017\frac{120}{17}​= 7.0588 ≈ 7 hours

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