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Math Help - SAT question.

  1. #1
    Senior Member vaironxxrd's Avatar
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    SAT question.

    This is a question taking from the SAT Question Of the Day.

    A mechanic can install carburetors in 3 cars every 4 hours. At that rate, how long will it take the mechanic to install carburetors in 5 cars?



    How can I do this. By the way tomorrow Is my SAT and I know I will do very poorly.

    ( Sorry if I posted this in the wrong section I din't know where is it suppose to go"
    Last edited by vaironxxrd; June 3rd 2011 at 03:29 PM. Reason: Section
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  2. #2
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    Quote Originally Posted by vaironxxrd View Post
    This is a question taking from the SAT Question Of the Day.

    A mechanic can install carburetors in 3 cars every 4 hours. At that rate, how long will it take the mechanic to install carburetors in 5 cars?



    How can I do this. By the way tomorrow Is my SAT and I know I will do very poorly.

    ( Sorry if I posted this in the wrong section I din't know where is it suppose to go"
    1 car done in 4/3 hours. Therefore ....
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  3. #3
    Senior Member vaironxxrd's Avatar
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    Quote Originally Posted by mr fantastic View Post
    1 car done in 4/3 hours. Therefore ....
    i said 3/4 = 5/x and I get 3x=4*5=20 therefore 20/3=6.66
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  4. #4
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    It will help on these tests just to write out that math in words sometimes, if you can think better that way.


    \frac{1(mechanic) "fixes"3 (cars)}{"every"4(hours)}



    \frac{1(mechanic)3(cars)}{4(hours)}= \frac{1(mechanic)5(cars)}{x(hours)}


    \frac{3(cars)}{4(hours)}= \frac{5(cars)}{x(hours)}


    and you know how to solve that math! Good luck on your SAT you'll do real well.
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  5. #5
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    A mechanic can install carburetors in 3 cars every 4 hours. At that rate, how long will it take the mechanic to install carburetors in 5 cars?
    one way to do this is to find out the rate
    rate=3/4per hours
    then assume x= how long will it take the mechanic to install carburetors in 5 cars
    3x/4=5
    x=20/3
    so the answer is 6+2/3 hours
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  6. #6
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    Quote Originally Posted by vaironxxrd View Post
    i said 3/4 = 5/x and I get 3x=4*5=20 therefore 20/3=6.66
    Yes. But surely it is obvious from my previous post that the answer is got simply by multiplying 4/3 by 5 ....!
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  7. #7
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    Remember:
    a in b
    c in ?

    ? = b/a * c
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  8. #8
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    The amount of cars repaired is directly proportional to the time given, so:

    3 cars : 4 hrs = 5 cars : x hrs

    And by simple multiplication, and by rearranging the equation you get:

     x = \frac{20}{3} ,

    which amounts to 6 hours 40 minutes.

    Good luck on your SAT.
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