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Math Help - Constructing a linear function.

  1. #1
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    Constructing a linear function.

    A photocopy store advertises the following prices: 5/c per copy for the first 20 copies, 4/c per
    copy for the 21st through 100th copy, and 3/c per copy after the 100th copy. Let
    x be the
    number of copies, and let
    y be the total cost of photocopying. (a) Graph the cost as x goes
    from 0 to 200 copies. (b) Find the equation in the form
    y = mx + b that tells you the cost
    of making
    x copies when x is more than 100

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  2. #2
    Grand Panjandrum
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    Re: I cant solve this simple problem

    Quote Originally Posted by sardorbek View Post
    A photocopy store advertises the following prices: 5/c per copy for the first 20 copies, 4/c per
    copy for the 21st through 100th copy, and 3/c per copy after the 100th copy. Let
    x be the
    number of copies, and let y be the total cost of photocopying. (a) Graph the cost as x goes
    from 0 to 200 copies. (b) Find the equation in the form y = mx + b that tells you the cost
    of making x copies when x is more than 100
    The graph consists of three line segments the first for 0 to 20 copies of slope 5c per copy. The second from 20 to 100 copies with slope 4c per copy starting from where the first segment ended. The third segment runs from 100 to 200 copies with a slope of 3c per copy starting from where the second segment ended.

    CB
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  3. #3
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    Re: I cant solve this simple problem

    Thank you for explanation,
    I tried to solve it but my answer was wrong. Answer should be according to the book y=0.03x+1.2.
    Does this function intersect at 1.2??
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  4. #4
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    Re: I cant solve this simple problem

    It's impossible to tell what you did wrong if you don't show what you did or even what result you got!

    How much will it cost to make 100 copies? that is 20 at 5 c each, 80 at 4 c each.

    How many will it cost to make 200 copies? Again, that is 20 at 5c each and 80 at 4 c each, plus 100 at 3 c each. Once you know the cost for 100 and 200,
    put those as "y" values in y1= m(100)+ b and y2= m(200)+ b and solve for m and b.

    (Yes, the y-intercept of this function is $1.20.)
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  5. #5
    Grand Panjandrum
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    Re: I cant solve this simple problem

    Quote Originally Posted by sardorbek View Post
    Thank you for explanation,
    I tried to solve it but my answer was wrong. Answer should be according to the book y=0.03x+1.2.
    Does this function intersect at 1.2??
    Did you do the first part and plot the graph?

    ..and as Halls asked what was your answer and argument to support it?

    By the way the book answer is wrong unless there is more in the question than you posted. The question is formulated in cents but the book answer given in dollars, now if it says it wants the answer in dollars that is different.


    CB
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  6. #6
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    Re: Constructing a linear function.

    Thank you HallsofIvy.
    I am agree with Captain Black. The question is not asked either in dollar or cent.
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