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Math Help - Car Deappreciation vs Kilometers done

  1. #1
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    Car Deappreciation vs Kilometers done

    Hi, i'm really disappointed with myself, i'm a 2nd year math student in university, and tutoring a 7th grader, and i couldnt figure this out.

    I have a graph, with car's resale value on y-axis, and kilometers done on it on x-axis.
    There's 2 linear relationships given, between x and y.
    Then it asks about the number of kilometers on the car, when its resale value is $0.
    The two lines form a continuous graph, but it's not perfectly a straight line, (The 2 have different equations). Then they stop at some point, and asks for x when y = 0.
    Is it a curve fitting problem, and if so... is that taught in 7th grade, i have no clue. Because i have to use techniques that are covered in his school, and my damn problem is that his textbook is in french. (in canada)
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  2. #2
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    Quote Originally Posted by Revolutionofidentity View Post
    Hi, i'm really disappointed with myself, i'm a 2nd year math student in university, and tutoring a 7th grader, and i couldnt figure this out.

    I have a graph, with car's resale value on y-axis, and kilometers done on it on x-axis.
    There's 2 linear relationships given, between x and y.
    Then it asks about the number of kilometers on the car, when its resale value is $0.
    The two lines form a continuous graph, but it's not perfectly a straight line, (The 2 have different equations). Then they stop at some point, and asks for x when y = 0.
    Is it a curve fitting problem, and if so... is that taught in 7th grade, i have no clue. Because i have to use techniques that are covered in his school, and my damn problem is that his textbook is in french. (in canada)
    Take the right most of the linear segments, extend that line until it meets the x-axis. That value of x is what is asked for.

    CB
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  3. #3
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    thanks.
    But how do i know that the slope of car's deappreciation is not going to change again after a certain point even after the right most straight line? I know the 7th grader might not have to consider such a possibility but i'm asking for my own knowlege.
    Thanks again
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  4. #4
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    Quote Originally Posted by Revolutionofidentity View Post
    thanks.
    But how do i know that the slope of car's deappreciation is not going to change again after a certain point even after the right most straight line? I know the 7th grader might not have to consider such a possibility but i'm asking for my own knowlege.
    Thanks again
    Because the question would tell you if it did.
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  5. #5
    Grand Panjandrum
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    Quote Originally Posted by Revolutionofidentity View Post
    thanks.
    But how do i know that the slope of car's deappreciation is not going to change again after a certain point even after the right most straight line? I know the 7th grader might not have to consider such a possibility but i'm asking for my own knowlege.
    Thanks again
    You don't, its an assumption that you have to make to get any sort of answer for this question as stated.

    You can of course make a different assumption but then you will be on you own.

    CB
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  6. #6
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    Quote Originally Posted by CaptainBlack View Post
    You don't, its an assumption that you have to make to get any sort of answer for this question as stated.

    You can of course make a different assumption but then you will be on you own.

    CB

    thank you.
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