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Math Help - simultaneous equations (?) power company question.

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    simultaneous equations (?) power company question.

    Hello.

    I have this question.

    one company charges a standing charge of 15 per quarter, with a cost of 9 per unit used, whereas another companycharges 10.5 per quarter, with a cost of 11 per unit.

    find out which number of units makes the cost of each company the same.
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    Quote Originally Posted by Paulotron
    Hello.

    I have this question.

    one company charges a standing charge of 15 per quarter, with a cost of 9 per unit used, whereas another companycharges 10.5 per quarter, with a cost of 11 per unit.

    find out which number of units makes the cost of each company the same.
    15+9x=10.5+11x
    Thus,
    15+9x-11x=10.5
    15-2x=10.5
    -2x=-4.5
    x=2.25
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    Quote Originally Posted by Paulotron
    Hello.

    I have this question.

    one company charges a standing charge of 15 per quarter, with a cost of 9 per unit used, whereas another companycharges 10.5 per quarter, with a cost of 11 per unit.

    find out which number of units makes the cost of each company the same.
    The first company charges
    y = 9x + 15 for x units per quarter.

    The second company charges
    y = 11x + 10.5 for x units per quarter.

    We need a number of units x that makes both of these expressions equal.

    You can do this in several ways. You can graph both cost functions and see for what value of x they intersect.

    The other way is algebraic. We have two equations for which we are setting the x and y values to be equal. Since the y values are equal we have:
    y = 9x + 15 = 11x + 10.5
    for some value of x. Solve this equation for x and you have your answer.

    -Dan
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