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Math Help - Finding how many revolutions a car will make dirving a certain amount of miles?

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    Finding how many revolutions a car will make dirving a certain amount of miles?

    Algebra II question, I've tried everything above and beyond unit conversions and I cannot figure this out. If someone would explain to me how to do this problem I would be very greatful. The lesson this homework is based off of is based on Direct / Inverse variations.

    You are going to drive 480 miles today at an average speed of 60 miles per hour. Thus you are going to drive for a total of (8) hours. The diameter of the wheels on your car (including tires) is 25 inches. Thus each wheel is going to turn a total of _______ times today.

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    e^(i*pi)'s Avatar
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    Quote Originally Posted by Lvl80 View Post
    Algebra II question, I've tried everything above and beyond unit conversions and I cannot figure this out. If someone would explain to me how to do this problem I would be very greatful. The lesson this homework is based off of is based on Direct / Inverse variations.

    You are going to drive 480 miles today at an average speed of 60 miles per hour. Thus you are going to drive for a total of (8) hours. The diameter of the wheels on your car (including tires) is 25 inches. Thus each wheel is going to turn a total of _______ times today.

    Circumference of a tyre : C = \pi D (where D is diameter)


    The distance covered in one resolution is equal to C

    Thus n_C = \dfrac{480}{C} \cdot k (where k is the conversion factor between inches and miles and k>1 )
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    Junior Member RHandford's Avatar
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    Hi

    Circumference = 2*pi*r
    Radius = 25/2
    1 mile = 63360 inches

    Can you continue from here?
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    Thanks both of you. For e^'s formula, I would plug in 78.5 for C (having done 25 * pi) then multiply it by 63360 / 1 mile to convert it into inches, right? Then the answer for Nc would be

    Nc = 480 / 78.5 * 63360 / 1, which = 10362 revolutions. Is this correct?
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    Ah, I found my error in the above post. In the above post I attempted to cross multiply, which I do not have to do. After doing

    Nc = 480 / 78.5 * 63360 / 1

    I got 387424 as my answer, which is correct. Thanks to both of you for helping me with this. The whole concept is still a bit foggy, but I'm getting it.
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  6. #6
    Junior Member RHandford's Avatar
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    480 miles is 480*63360=30412800 inches.
    1 revolution is 2*pi*r=2*3.142*12.5=78.5389 inches
    Total revolutions is 30412800/78.5389=387228
    So each wheel will travel 387,228 revolutions.
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    e^(i*pi)'s Avatar
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    n_C = \dfrac{480}{25\pi} \cdot 63360 = 387227

    I don't know if your book told you to round pi off to a certain value, if so use that value and disregard this one.

    Normally, you'd not round off until the end of a sum
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