spring2008stat201-hw09KEY

# spring2008stat201-hw09KEY - 36-201 Spring 2008 Homework 9...

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This document available on: http://www.stat.cmu.edu/~gordonw/spring2008stat201.html 36-201 Spring 2008 Homework 9 – KEY

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Stat 201 Spring 2008 Page 1 of 7 Homework 9 – KEY This document available on: http://www.stat.cmu.edu/~gordonw/spring2008stat201.html Due: Wednesday, April 2 , at the beginning of lecture. Homework considered late beyond the first 10 minutes of lecture. Late Homework Policy: Late homework may be turned-in for a maximum of half credit, up to 4:00 PM on the same Wednesday the homework is due. Late homework should be placed in the manila envelope which will be posted by room 328-C, Facilities Management Building (FMS). Late homework should be labeled with the course as well as your name. Please do not turn in any homework to any mailboxes. Please include the top-page ‘coversheet’, filled-out and stapled to your homework. Show all work. This homework covers chapter 7 in the course textbook. Point Distribution: Exercise 1 Exercise 2 Exercise 3 Exercise 4 effort & neatness TOTAL 35 10 13 22 20 100 NOTE: To save paper, you are encouraged to print double-sided (‘duplex’ mode).
Stat 201 Spring 2008 Page 2 of 7 Homework 9 – KEY This document available on: http://www.stat.cmu.edu/~gordonw/spring2008stat201.html 1. [confidence interval for mean] Suppose a company wants to estimate μ , the mean number of weekly hours that U.S. adults use computers at home. Suppose a random sample of 49 U.S. adults gives a mean weekly computer usage time of 11 . 25 hours. Suppose that, from prior studies, the population standard deviation is assumed to be σ = 3 . 5 hours. 1 (a) (i) What is the sample in this scenario? The 49 adults. (or similar wording) (ii) What is the population in this scenario? All U.S. adults (iii) What is the symbol that represents the unknown parameter of interest, and what does that symbol refer to in this scenario? Symbol: Meaning: The (true) population mean number of hours that all U.S. adults use computers at home. 1 (b) What is the ‘point estimate’ for in the scenario? [Give both its value and the symbol.] Symbol: x Value: 11.25 1 (c) Briefly say why the conditions for constructing a confidence interval will be satisfied in this case. Answer: Sampling random (as stated in the exercise) The Central Limit Theorem condition for ‘means’ is satisfied, because the sample size of 49 is greater than or equal to 30 [exercise 1 continues on next page]

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Stat 201 Spring 2008 Page 3 of 7 Homework 9 – KEY This document available on: http://www.stat.cmu.edu/~gordonw/spring2008stat201.html
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## spring2008stat201-hw09KEY - 36-201 Spring 2008 Homework 9...

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