Enjoy learning Statistics Online! Please be sure to share and subscribe to our YouTube channel.
ASK THE PROFESSOR FORUM
Course Documents
Chapter 1 - Intro
Chapter 2 - Methods for Describing Sets of Data
Chapter 3 - Probability
Chapter 4 - Discrete Random Variables
Chapter 5 - Normal Random Variables
Chapter 6 - Sampling Distributions
Chapter 7 - Confidence Intervals
Chapter 8 - Tests of Hypothesis: One Sample
Chapter 9 - Confidence Intervals and Hypothesis Tests: Two Samples
Sample Exam I: Chapters 1 & 2
Sample Exam II: Chapters 3 & 4
Sample Exam III: Chapters 5 & 6
Sample Exam IV: Chapters 7 & 8
Hi! I am doing number 48 and for some reason I don't get the answer posted on the hw, i get 1.07, 5.13. However, when I do it on my graphing calculator like you did in the video, I get the right answer. I was wondering if you had a video of you doing the problem w/o the graphing calculator so I could see where I am doing it wrong.
Posted to STATS 2 on Sunday, September 14, 2014 Replies: 2
Hi Ruby,
The mistake you are making is that you are not using the t critical value like you are supposed to use. You are using the z critical value. In step 2 of the problem, you are going to the t table and looking up 0.005 in one tail (for 99% confidence), which is correct, but then you go straight to the bottom of the table to get the critical z value 2.576.
That is your error. Instead of going to the bottom of the t table, you should be stopping in the 28 degrees of freedom row because your sample size is only 29. Remember for 30 or less, we will use the t critical value with n - 1 degrees of freedom, not the z critical value which is found in the last row of the table.
If you use the correct critical value, your margin of error will look like this:
2.763 * 4.25/SquareRoot(29) = 2.18057
Then you can add and subtract this margin of error to and from the mean to get the right interval.
Hope that makes sense,
Professor McGuckian