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8 September, 01:13

It takes an older pump 3 times as long to drain a certain pool as it does a newer pump. Working together, it takes the two pumps 9 hours to drain the pool. How long will it take the older pump to drain the pool working alone?

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  1. 8 September, 01:36
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    36hrs

    Step-by-step explanation:

    Let the older pump be "a" and the newer pump be "b"

    3a = b

    3a + b = 9

    We simply put the value of b from equation 1 into equation 2

    3a + (3a) = 9

    6a = 9

    a = 1.5

    If a = 1.5

    3 (1.5) = 4.5

    b = 4.5

    If a and b do it in 9hrs, it means they both contribute 4 parts to each hour's progress. 60minutes/4 = 15minutes a part.

    So the new pump does in 15minutes what the old pump does in 45minutes

    Ratio 3:1 = 4 NB: ratio 3 is for the new pump because it is 3 times as efficient.

    So the old pump working alone will require 9*4 = 36hrs
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