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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

Professor,
I need help with question 18 from section 9.4. Could you please show how you get the test stat of 11.44, I get something different.
Thank You.

Posted to STATS 2 on Wednesday, October 9, 2013   Replies: 3


Professor Mcguckian
10/09/2013
1:06 PM EST

Hi Peggy,

I can create a video for this later, but for now, let me just explain here:

Because we assume equal variances for this problem, we first need to calculate Sp²

Sp² = [(n1-1)*S1² + (n2-1)*S2²]/(n1 + n2 - 2)

(27*4.51² + 28*3.98²)/(28+29-2) = 18.04934364 = Sp²

Then our test stat formula for this problem would be:

t = (Xbar1 - Xbar2) / SqrRoot(Sp²/n1 + Sp²/n2) = (38.28 - 25.4) / SqrRoot(18.04934/28 + 18.04934/29) = 11.443

Note: the denominator part of the test stat (the part under the squareroot) should be 1.125615643. Use that to check your calculation.

Hope that helps,

Professor

 


Professor Mcguckian
10/09/2013
7:17 PM EST

Hi Peggy,

Here is a video explanation of how to work out the test statistic:

 

 


.
10/09/2013
9:05 PM EST
Thank you Professor. I see what I was doing wrong now.

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