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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

Hello Professor disregard the question I just asked " in the homework section 9.8 problem 35 I am not getting the right numbers for the interval. My critical value is 3.106 and the test stat comes out to be 3.16. What am I doing wrong?" my critical value was incorrect now I have the interval [-3.24, 1.24].

Posted to STATS 2 on Wednesday, October 8, 2014   Replies: 1


Professor Mcguckian
10/08/2014
6:00 PM EST

Hi Sheyla,

When I subtract the two rows of data (Reported - Measured), I get an average difference of -1.0.

The data for this problem is then:

n = 12

X-bar = -1.0

S = 3.5196

CL = 0.95

The critical ta/2, df value is: t0.025, 11 = 2.201

This gives us a margin of error of: E = 2.201*3.5196/root(12) = 2.2363.

The final interval is (-1.0 - 2.2363, -1.0 + 2.2363) = (-3.2363, 1.2363).

**note: if I had done my subtraction in the other order, I would have the answer: (-1.2363, 3.2363).

I hope this answers your question,

Professor McGuckian

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