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Seeming paradox when squaring distance depending on units

  1. Feb 28, 2014 #1
    Hello all

    This is probably simple and I'm overlooking something

    1 mile = 5280 feet

    10% of a mile is 528 feet

    528 feet squared is 278,784 feet which is 52.8 miles squared

    But 0.1 miles squared is .01 miles squared

    So depending on if you square it as 0.1 miles, or if you convert it to feet, then square it and convert it back, you get wildly different answers

    Why is this.? Not sure why I thought of this.

    Thanks in advance
  2. jcsd
  3. Feb 28, 2014 #2
    You used the wrong conversion factor.

    First of all, (528 feet)2 is not equal to 278784 feet. It is equal to 278784 feet2.

    In any case, you want to convert this to a value in miles2.

    Now, the conversion factor between feet2 and miles2 is not the same as the conversion factor between feet and miles, because feet2 are not the same as feet, and miles2 are not the same as miles. In fact, the conversion factor is 27878400 feet2 = 1 mile2, and if you use this correct conversion factor you will get the correct answer of 0.01 miles2.
  4. Feb 28, 2014 #3
    That should be feet squared.

    ##\frac{278784 ft^2}{1} \cdot \frac{(1 mi)^2}{(5280ft)^2} = 0.01 mi^2##
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