ST361 HW6 (due Thursday 10/24/13)
(a) Show your work in order to earn the full credit. This means that you have to present your
steps or explain your reasoning for the answers you obtain, rather than just to write down the
answer itself.
Note that answers without steps or reasoning will receive 0 credits even if the answers are
correct!
(b) Remember to staple your homework and write your name on your homework. You’ll
lose 5 points if not.
---------------------------------------------------------------------------------------------------------1) 5.46 (p.237) (b) Also report what the sampling distribution of the sample mean is
2) 5.49 (p.237) (b)
3) 5.52 (p.237)
4) A random sample of 10 houses in a particular city is selected and each of the houses’ level of
radon gas is measured. The values collected are given listed below in pars per million (ppm)
4, 8, 13, 7, 6, 3, 9, 8, 11, 8.
10
Note that
x
i 1
i
 77 and
10
x
i 1
2
i
 673 .
(a) Give a point estimate for   the average level of radon gas in a house in this city.
(b) Is your point estimate in (a) an unbiased estimator? Why or why not?
(c) Give a point estimate for  =the SD of the level of radon gas in a house in this city
(d) Report the S.E. of your point estimate in (a).
5) 7.11 (p.301) (a)(b)(d)
Hint for (d): The statement means that exactly 95 of the resulting intervals will include .
6) A company is collecting samples containing 25 boxes every 10 minutes. Assume that during a
5-day period, there are 720 samples collected and based on which, 700 confidence intervals
were constructed for estimating the mean box weight (). If the level of the confidence is 90%
for each of the 720 intervals, how many of the intervals would you expect that fail to cover ?
1