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Thread: help forming this equation

  1. #1
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    help forming this equation

    A plumber charges 70 for 2 hours job and 145 for 5 hours job. Find $\frac{\mathrm{dc} }{\mathrm{d} t}$
    How do i form an linear equation from this information.

    I did this $ C = \frac{70t}{2} + \frac{145t}{5}$ but it leads to $ C = \frac{32}{5}t$

    Therefore, i did not get the right answer.

    Please help
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  2. #2
    MHF Contributor
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    Re: help forming this equation

    You have two points

    $p_1 = (2,70),~p_2 = (5,145)$

    the slope is given by

    $m = \dfrac{145-70}{5-2} = \dfrac{75}{3} = 25$

    Using point slope form with $p_1$ we have

    $y-70 = 25(x-2)$

    $y = 25x + 20$
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