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Math Help - Map legend

  1. #1
    Newbie Steves5a's Avatar
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    need assistance

    on a map, 1 1/2 inches represent 45 miles. if two cities are 5 inches apart on the map, how far are they apart.

    A quality control inspector expamine 42 light bulbs and 7 were defective. at this rate, how many defectives will there be in a lot of 2682.


    dont need the answers but need to know how to work them
    Last edited by MathGuru; August 27th 2005 at 12:05 PM.
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  2. #2
    Senior Member
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    This is what I was taught to call the "Rule of Three".

    If 1 1/2 inches represents 45 miles then 1 inch represents 45/(1 1/2) miles. To simplify 45/(1 1/2) multiply top and bottom by 2 to give 90/3 = 30. So 1 inch represents 30 miles. Now 5 inches represents ...

    Similarly, if 7 out of 42 bulbs are defective then that is a rate of 1 in 42/7 = 1 in 6 or 1/6 in 1. So out of 2682 bulbs expect (1/6) times 2682 = 2682/6 = ...
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