Chapter 7 Good Questions Answered

Chapter 7 Q20b

Q. Mean length of employment is 17.5 weeks and population standard deviation is 4 weeks. You take a sample of 50 unemployed individuals for a follow-up study. What is the probability that the sample will provide a sample mean within one week of the population mean?

A. This question is asking you to find the area (which represents a probability) one week either side of the population mean. In Excel, go:

=norm.dist(18.5,17.5,4,true) – normdist(16.5,17.5,4,true)

Chapter 7 Q44

Survey results give the standard error of the mean as 20. The population standard deviation is 500.

a.       How large was the sample used? Answer: the SE = standard deviation/root n. So root n = standard deviation/SE. Here root n = 500/20 = 25. So n = 25 squared.

b.      What is the probability that the point estimate was within plus/minus 25 of the population mean?

 Answer: we are looking for the area between the population mean plus 25 and the population mean minus 25. The population mean isn`t given, but this doesn`t matter. Use any number you like. Here I`ve used 100.  In Excel: =norm.dist(125,100,500,true)-norm.dist(75,100,500,true)