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Math Help - Proportion

  1. #1
    Member
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    Proportion

    I need a simple way to solve this question.

    It takes 3 men to gig 2 identical trenches in 5 hours .If all the men work at the same rate ,how long will it take 5 men to dig 7 of these trenches ?

    i have solved it this way through the help of an example in the book.

    Solution

    First we keep the number of trenches constant

    No of men --- No of trenches --- No of Hours

    3 --- 2 --- 5

    1 --- 2 --- 5*3

    5 --- 2 --- (5*3)/5=3

    Next we keep the number of men constant


    No of men --- No of trenches --- No of Hours
    5 --- 2 --- 3

    5 --- 1 --- 3/2=1.5

    5 --- 7 --- 1.5*7=10.5

    Therefore 5 men will take 10.5 hours to dig 7 identical trenches.


    I want a simpler solution to this.
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  2. #2
    MHF Contributor
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    Establish units.

    2 trenches = 15 man-hours

    7 trenches * (15 man-hours / 2 trenches) = (105/2) man-hours

    (105/2) man-hours / 5 men = (21/2) hours

    Same solution, really. Why do you think there is an easier solution? Perhaps your "want" is unreasonable. Unique solutions do not care how you find them.
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