University of California at Irvine
Department of Statistics
Statistics 67
Winter Quarter 2016
Homework 5. SOLUTION.
1. (10 points) In order to ensure efficient usage of a server, it is necessary to estimate the mean
...
University of California at Irvine
Department of Statistics
Statistics 67
Winter Quarter 2016
Homework 5. SOLUTION.
1. (10 points) In order to ensure efficient usage of a server, it is necessary to estimate the mean
number of concurrent users. According to records, the average number of concurrent users at
100 randomly selected times is 37.7, with a standard deviation σ = 9:2
(a) (5 points) Construct a 90% confidence interval for the expectation of the number of concurrent users.
(b) (5 points) At the 1% significance level, do these data provide significant evidence that the
mean number of concurrent users is greater than 35?
Answer:
2. (10 points) Installation of a certain hardware takes random time with a standard deviation of
5 minutes.
(a) (5 points) A computer technician installs this hardware on 64 different computers, with
the average installation time of 42 minutes. Compute a 95% confidence interval for the
population mean installation time.
(b) (5 points) Suppose that the population mean installation time is 40 minutes. A technician
installs the hardware on your PC. What is the probability that the installation time will
be within the interval computed in (a)?
Answer:
3. (25 points) A survey asked students their heights and whether they preferred to sit in the front,
middle, or back of the class. The following data are the heights of the 15 females in the sample
who said they prefer to sit in the back.
68, 62, 65, 69, 68, 69, 64, 66, 69, 68, 62, 64, 67, 68, 65
The mean height for the population of college females is 65 inches. Does this sample provide
a significant evidence that females who prefer to sit in the back of the room are taller than
average? Use a α = 0:05.
(a) (5 points) What is the sample mean height X¯?
(b) (5 points) What are the null and alternative hypotheses being tested? Write them in
symbols and define your symbols.
(c) (5 points) What is the null standard error ?
(d) (5 points) Compute the values of test statistics and test p{value.
(e) (5 points) What conclusion would be made in this situation?
Answer:
[Show More]