# Thread: Need help ASAP 20 mins!

1. ## Need help ASAP 20 mins!

Sorry for the quick need of help, but can you guys help me solve this problem? I have tried for over 2 hours and still can't find the answer, and I need to submit the correct answer in 20 mins:

The following data list ages of cars (in years) and monthly repair cost. What is the standard error of estimate?
Age Cost
3 25
5 35
7 55
9 50
11 75
14 85

a. 7.34
b. 5.49
c. 6.36
d. 8.75

I used the formula to find the regression line, and then calculated (y-y')2 and substituted into the Sest formula but none of those answer show up.

Help is GREATLY appreciated!

Thanks

2. ## Re: Need help ASAP 20 mins!

What did you get for your regression line?

9.12 + 5.51x

4. ## Re: Need help ASAP 20 mins!

What was the answer you thought it should be by the way? Also, just for clarification when you say standard error do you mean the estimate of the standard deviation about the regression line or do you mean the standard error of the estimate of the slope or the standard error of the estimate of the intercept? My guess is the standard deviation around the regression line (ie the residual standard error).

5. ## Re: Need help ASAP 20 mins!

I thought the answer should be 5.26. I'm not entirely sure, but it describes it in the textbook as "The standard error of the estimate, denoted be Sest, is the standard deviation of the observed y values about the predicted y' values."

I have to hand this in in 10 mins! Thanks for the help!

6. ## Re: Need help ASAP 20 mins!

Would you mind giving me the answer so I can hand the right one in? Would really appreciate!

7. ## Re: Need help ASAP 20 mins!

That's not really how I operate. I feel for you but I'm not at liberty to just hand out answers.

But if it helps a little here's some R code I used to get (almost) to the answer. Maybe you just had an arithmetic error or something.

Code:
``````> hat <- 9.12 + 5.51*x\$age
> hat
[1] 25.65 36.67 47.69 58.71 69.73 86.26
> x\$cost - hat
[1] -0.65 -1.67  7.31 -8.71  5.27 -1.26
> (x\$cost -hat )^2 / 4
[1]  0.105625  0.697225 13.359025 18.966025  6.943225  0.396900
> sum((x\$cost -hat )^2) / 4
[1] 40.46802``````

8. ## Re: Need help ASAP 20 mins!

Would you help me solve it soon! Thanks! I do apologize for asking, I am just getting a little frustrated becasue I have been working at this for about 2 hours, along with 2 other questions!

9. ## Re: Need help ASAP 20 mins!

Your Regression line is correct. Answer is 6.3611 which is the standard error of the estimate.

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