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Math Help - need help

  1. #1
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    need help

    . You can determine the speed of a car by measuring the time it takes to travel between mile markers on a highway. (a) How many seconds should elapse between two consecutive mile markers if the carís average speed is 65 mi/h? (b) What is the carís average speed if it takes 65 s to travel between the mile markers?
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by cruzangyal View Post
    . You can determine the speed of a car by measuring the time it takes to travel between mile markers on a highway. (a) How many seconds should elapse between two consecutive mile markers if the car’s average speed is 65 mi/h? (b) What is the car’s average speed if it takes 65 s to travel between the mile markers?
    Note that 1 hour = 3600 seconds


    The car is moving at the same speed, so it's speed is constant.

    Now, \mbox {Speed} = \frac { \mbox { Distance }}{ \mbox { Time }}

    The distance the car travels in 3600 seconds is 65 miles, how many seconds does it take to travel 1 mile moving at the same speed. Since the speeds must be equal, we can equate the formulas:

    Let the amount of seconds the car takes to travel 1 mile be x.

    \frac { \mbox { Distance}_1 \mbox { }}{ \mbox { Time}_1 \mbox { }} = \frac { \mbox { Distance}_2 \mbox { }}{ \mbox { Time}_2 \mbox { }}

    \Rightarrow \frac {65 \mbox { miles }}{ 3600 \mbox { seconds }} = \frac {1 \mbox { mile }}{x \mbox { seconds }} .........Now we solve for x

    \Rightarrow 65x = 3600 .................................I cross-multiplied (I left out the units).

    \Rightarrow x = \frac {3600}{65} \approx 55.38 \mbox { seconds }



    Part (b) is similar
    Last edited by Jhevon; June 22nd 2007 at 11:32 AM.
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