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Thread: distance over time

  1. #1
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    distance over time

    a student walks y kilometres at 3km/h

    i) write down an expression for the time, in hours that he takes.

    ii) he then walks a further y+3 kilometres at 4km/h. the total walking time is 4 hours and 50 minutes. write down the equation in y and solve it.
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  2. #2
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    Quote Originally Posted by simonmann View Post
    a student walks y kilometres at 3km/h

    i) write down an expression for the time, in hours that he takes.

    ii) he then walks a further y+3 kilometres at 4km/h. the total walking time is 4 hours and 50 minutes. write down the equation in y and solve it.
    $\displaystyle speed=\frac{distance}{time}$

    Solve for time: $\displaystyle \frac{y}{t}=3~\implies~t=\frac y3$

    The next part of his walk:

    $\displaystyle \frac{y+3}t=4~\implies~ t=\frac{y+3}4$

    Both periods together are $\displaystyle \frac{29}6\ h$

    $\displaystyle \frac y3 + \frac{y+3}4 = \frac{29}6$

    Solve for y. I've got: $\displaystyle \boxed{y = 7\ km}$
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  3. #3
    A riddle wrapped in an enigma
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    distance = rate*time

    $\displaystyle d=rt$

    $\displaystyle t=\frac{d}{r}$

    $\displaystyle t_1=\frac{y}{3}$
    $\displaystyle t_2=\frac{y+3}{4}$

    $\displaystyle t_1+t_2=\frac{y}{3}+\frac{y+3}{4}=\frac{29}{6}$

    $\displaystyle 4y+3y+9=58$

    $\displaystyle 7y=49$

    $\displaystyle y=7km$


    Too fast for me Earboth!!
    Last edited by masters; May 28th 2008 at 06:51 AM.
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