## StClowers one year ago Height (ft) Interval after (min) 96 68 111 80 76 66 91 72 66 58 108 79 116 84 91 79 The data show the time intervals after an eruption (to the next eruption) of a certain geyser. Find the regression equation, letting the first variable be the independent (x) variable. Find the best predicted tie of the interval after an eruption given that the current eruption has a height of 84 feet. Use a significant level of 0.05. A. What is the regression equation? Ŷ = __ + ___x B. What is the best predicted value? Ŷ ͌ __ minutes

1. mathmale

Have you found a regression equation before? Do you happen to have a TI-84 calculator available to you?

2. StClowers

i do have one

3. mathmale

Have you used it before to calculate a regresstion line in the form y=ax+b?

4. StClowers

i am a rookie at it so i have not

5. mathmale

Have you previously used the STAT key, which brings up a menu, one of the items on which says EDIT?

6. StClowers

yes

7. mathmale

If you'd press STAT and then EDIT, your calc will display a couple of columns. would you try that, please? are there numbers in the columns, or are they empty?

8. StClowers

im there

9. StClowers

there are numbers under L2

10. mathmale

If you know how to clear out the numbers in column L2, please do it. Otherwise we may be able to find the regression line without clearing L2.

11. StClowers

ok cleared

12. mathmale

Here's your data: 96 68 111 80 76 66 91 72 66 58 108 79 116 84 91 79 copy everything from the 1st col. into L1; copy everything from the 2nd col. into L2. Any questions about this, please ask.

13. StClowers

done

14. mathmale

Now press STAT again. You should see a menu; the middle item at the very top should say MATH or CALC. Does it?

15. StClowers

yes

16. mathmale

Please move the cursor to cover MATH OR CALC.

17. StClowers

ok done

18. mathmale

tHEN press the character " 4 ". Your calculator will exevcute option #4, whivch is "linear regressin Line" or something like that.

19. StClowers

ok done

20. mathmale

Does it display a value for a and a value for b?

21. StClowers

yes it does

22. mathmale

cool. You're right up there with the best.

23. mathmale

what is a? what is b?

24. StClowers

well i hit enter and it went to LinReg(ax+b) and thats it

25. mathmale

have you pressed ENTER yet?

26. StClowers

yes

27. mathmale

Has the calc. responded with ifnormation / information?

28. StClowers

oh yes it has...i had to hit enter again...it says: y=as+b a= .4601084431 b= 29.82726569

29. StClowers

ab not as

30. mathmale

What we're hoping for is a screen that gives you... cool. Now write this equation: y=0.461x + 29.827. That is your regression equation.

31. StClowers

yay! That was it, now its asking me the next question

32. mathmale

This problem asks for the regression equation in slightly different format. It asks that you present b first, and then a. So, to asnwer this quaetion, type in 29.827 for the first blank and 0.461 in the 2nd blank. How

33. mathmale

Cool!

34. mathmale

Now write down on paper that same regression equation.

35. StClowers

thats exciting! lol

36. mathmale

type here what the 2nd question asks you for.

37. StClowers

ok. What is the best predicted value? Ŷ ͌ __ minutes

38. mathmale

Thisis very important: You're going to use the regression equation to PREDICT what the value of y (actually, of "y hat") is when x = 84, was it? Go back to the original question and ascertain the x value.

39. StClowers

84

40. mathmale

On paper, write the regression equation, subbing 84 for x. Calculate y hat.

41. StClowers

ok got it

42. mathmale

You're done! My regret is that we don't have time to review this whole problem so that every quantity and concept is clear to you. Hope you'll review our conversation and take notes on it so that you'll be able to do problems like this on your own.

43. StClowers

it says 68.551

44. StClowers

wow! Thank you so much. I have the others posted but we can do those tomorrow. I REALLY appreciate your help!!

45. mathmale

As much as I'd like to continue, it's past my bedtime! Don't know when I'll be available tomorrow, but I do expect to be on then and now. I'm so glad you've gotten this one problem behind you and are feeling better. You're most welcome!

46. StClowers

but one more thing: It ask me to round one decimal place so that would be 69, correct?

47. mathmale

No, that'd be 68.6. That's to 1 decimal place accuracy.

48. StClowers

oh gotcha, ok thanks you again! Gnight!! This really helps. I feel better

49. mathmale

Again, I'm so glad! Good night. Bye for now! Over and out.

50. StClowers

lol bye