# Car Deappreciation vs Kilometers done

• May 6th 2010, 09:59 PM
Revolutionofidentity
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)
• May 7th 2010, 11:21 PM
CaptainBlack
Quote:

Originally Posted by Revolutionofidentity
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
• May 8th 2010, 09:45 AM
Revolutionofidentity
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
• May 8th 2010, 03:30 PM
mr fantastic
Quote:

Originally Posted by Revolutionofidentity
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.
• May 8th 2010, 09:03 PM
CaptainBlack
Quote:

Originally Posted by Revolutionofidentity
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
• May 9th 2010, 11:21 AM
Revolutionofidentity
Quote:

Originally Posted by CaptainBlack
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.