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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, I am also stuck in 46 in section 8.6.

when i am finding p̂, i do not know if i do 15/100 or if its just 15.
If i use 15/100 in the formula to calculate the test statistic i get -1.40 and that is not correct? would you not do that for this problem?

thank you

Posted to STATS 1 on Tuesday, December 10, 2013   Replies: 5


Professor Mcguckian
12/10/2013
9:57 PM EST
Hi Natassia,

A professor claims that at most 10% of the class gets A’s each semester in his course. A random sample of 100 students from previous terms show that he gave out 15 A’s. Using a 5% significance level, test the professor’s claim.

Claim: p 0.10

Ho: p 0.10

Ha: p > 0.10

n = 100

x = 15

p-hat = x/n = 15/100 = 0.15

alpha = 5%

Test stat: (0.15 - 0.10) / Root(0.10 * 0.90 / 100) = 1.66666667 = 1.67

Critical value: 1.645

Reject H0, support Ha

We reject the claim since it is the same as H0 and we are rejecting H0.

 

Hope that helps,

Professor McGuckian


.
12/11/2013
12:26 AM EST
Yes thank you, i caught my mistake was i was following the formula wrong. I was placing p-hate in the wrong spot, and I thought had to find the q for the p-hat and that is why i was getting it wrong. THank you.

.
12/11/2013
12:34 AM EST
Professor, after finishing the sample exam, i find myself sometimes making the mistake when i arrive to the p-value what table i am supposed to use if the z-table or t-table. For example in question 15, i thought i would of had to use the z-table because N is a large number, but i had to use the t-table. Is there something that can be clarified so i can understand which one to use? thanks again

Professor Mcguckian
12/11/2013
12:44 AM EST

I think you are asking about the critical value because you cannot use the t-table to find a p-value (not an exact one anyway).

Remember that the t-table has z-values in the last row, so we almost always use the t-table to find critical z-values. If the sample size is large, we go to the last row of the table. If the sample size is small, we only go down to the appropriate degrees of freedom.

Of course, it is possible that your alpha value will not be on the t-table if your sample size is large because only 5 alpha values can be found on the t-table. If that happens, you will use the z table.  Section 8.2 covers this with several examples.


.
12/11/2013
2:39 PM EST
Ok thank you so much. I understand now

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