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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

Ask the Professor Forum

Hi Professor, From #42 of the 7.4 HW, the degrees of freedom is 127 and that number is not on the t-table so I don't know how to get the answer appropriately.
please help, thank you.

Posted to STATS 1 on Thursday, November 21, 2013   Replies: 2


Professor Mcguckian
11/21/2013
11:45 AM EST
Hi Christina,

In that section, you are trying to distinguish between when to use a z-critical value or a t-critical value. Remember, we are using the simplified rule that states if n > 30, we will find a z-critical value, otherwise we will find a t-critical value.

In the problem you asked about, since n = 128, we need a z-critical value, so you do not need to find degrees of freedom to find the 1.282. All you need to do is to find alpha/2 and go to the t-table. The answer you need will appear in the last row of the table.

Hope that answers your question,

Professor McGuckian


.
11/21/2013
10:36 PM EST
thank you!

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