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Math Help - Find Average Rate of Speed

  1. #1
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    Find Average Rate of Speed

    Maryann drove 280 miles to attend a marine biologist conference and arrived 1 hour late. Maryann figured out that, had she increased her average speed by 5 mph, she would have arrived on time. What was her average rate of speed?

    Isn't the average rate found using r = D/t?

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  2. #2
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    Quote Originally Posted by magentarita View Post
    Maryann drove 280 miles to attend a marine biologist conference and arrived 1 hour late. Maryann figured out that, had she increased her average speed by 5 mph, she would have arrived on time. What was her average rate of speed?

    Isn't the average rate found using r = D/t?
    Yes, that is the equation to use. How far have you gotten in applying it?

    . . .actual:
    . . . . .distance: 280
    . . . . .rate: r
    . . . . .time: 280/r

    . . .possible:
    . . . . .distance: 280
    . . . . .rate: r + 5
    . . . . .time: ..?..

    Complete the table. Then note the relation: "(possible time) is (actual time) less (one hour)". Translate this into an equation, and solve the rational equation for the value of "r".

    If you get stuck, please reply with a clear listing of your steps and reasoning so far. Thank you!
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  3. #3
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    here it is...

    Quote Originally Posted by stapel View Post
    Yes, that is the equation to use. How far have you gotten in applying it?

    . . .actual:
    . . . . .distance: 280
    . . . . .rate: r
    . . . . .time: 280/r

    . . .possible:
    . . . . .distance: 280
    . . . . .rate: r + 5
    . . . . .time: ..?..

    Complete the table. Then note the relation: "(possible time) is (actual time) less (one hour)". Translate this into an equation, and solve the rational equation for the value of "r".

    If you get stuck, please reply with a clear listing of your steps and reasoning so far. Thank you!
    possible time = D/r, which is the same as 280/(r + 5) = t



    The equation becomes: 280/(r + 5) = 280/r - 1

    I pretty much can do the rest. I have trouble, like most people, setting up the right equation from the information given in certain word problems. This is a common problem with students. Do you have questions involving average rate of speed in your purplemath website?
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