STAT 200, 2012 EDITION

STAT 200 QUIZ 3                                                Section 6384   Fall 2012 

I have completed this assignment myself, working independently and not consulting anyone except the instructor.                                        

NAME_____________________________

INSTRUCTIONS

·         The quiz is worth 40 points total. 

·         The quiz covers Chapters 7 and 8.

·         Make sure your answers are as complete as possible and show your work/argument.  In particular, when there are calculations involved, you should show how you come up with your answers with critical work and/or necessary tables.  Answers that come straight from program software packages will not be accepted. 

·         The quiz is open book and open notes. This means that you may refer to your textbook, notes, and online course materials, but you must work independently and may not consult anyone. The brief honor statement is on top of the exam. If you fail to put your name under the statement, your quiz will not be accepted. You may take as much time as you wish, provided you turn in your quiz via WebTycho by 11:59 pm EDT on Sunday, October 7.

1.  (15 points)  Mimi was the 5th seed in 2012 UMUC Tennis Open that took place in August.  In this tournament, she won 83 of her 100 serving games. Based on UMUC Sports Network, she wins 80% of the serving games in her 5-year tennis career.

(a) (3 pts) Find a 95% confidence interval estimate of the proportion of serving games Mimi won. (Show work)

(b) (2 pts) Based on the confidence interval estimate you got in part (a), is this tournament result consistent with her career record of 80%?  Why or why not?  Please explain your conclusion.

(c) (2 pts) A sport reporter commented that Mimi’s performance in the tournament is better than usual. You decide to test if the reporter’s claim is valid by using hypothesis testing that you just learned from STAT 200 class. What are your null and alternative hypotheses?

(d) (2 pts) What is the test statistic? (Show work)

(e) (2 pts) What is the P-value? (Show work)

(f) (2 pts) What is the critical value? (Show work)

(g) (2 pts) What is your conclusion of the testing at 0.05 significance level? Why?

2.  (6 points)  A simple random sample of 120 SAT scores has a mean of 1540. Assume that SAT scores have a population standard deviation of 333.

(a) (4 pts) Construct a 95% confidence interval estimate of the mean SAT score. (Show work)

(b) (2 pts) Is a 99% confidence interval estimate of the mean SAT score wider than the 95% confidence interval estimate you got from part (a)? Why? [You don’t have to construct the 99% confidence interval]

3.  (6 points)  Consider the hypothesis test given by                                              

In a random sample of 70 subjects, the sample mean is found to be  The population standard deviation is known to be      

(a)  (4 pts) Determine the P-value for this test.  (Show work)

(b)  (2 pts) Is there sufficient evidence to justify the rejection of  at the  level? Explain.                             

4. (7 pts) The playing times of songs are normally distributed. Listed below are the playing times (in seconds) of 10 songs from a random sample. Use a 0.05 significance level to test the claim that the songs are from a population with a standard deviation less than 1 minute.

448   231  246  246  227  213  239  258  255  257

(a) (1 pts) What are your null hypothesis and alternative hypothesis?

(b) (4 pts) What is the test statistic? (Show work)

(c)  (2 pts) What is your conclusion? Why? (Show work)

5. (6 pts) Given a sample size of 25, with sample mean 736.2 and sample standard deviation 82.3, we perform the following hypothesis test.

What is the conclusion of the test at the level?  Explain your answer. (Show work)