Statistics 104 – Homework 12
Due Thursday, December 8, 2011
Homework is due on the due date at the end of the lecture.
Reading:
November 17 – December 1 Sections 8.3 and 9.3
December 6 – December 8 Sections 10.2 and 10.4
Assignment:
1. Complete the following problems from the text: 8.27, 8.28, 8.29, 8.30, 9.29, 9.31 and
9.32.
Count
2. The strengths of plastic welds, in Newtons (N), for a random sample of 40 pieces of
plastic are summarized in the JMP output below.
Weld Strength (N)
Five Number Summary
Sample Statistics
100.0% maximum
18.30 Mean
16.43
75.0%
quartile
17.22 Std Dev
1.032
50.0%
median
16.49 N
40
25.0%
quartile
15.62
0.0%
minimum
14.28
a) Describe the shape of the histogram of weld strength.
b) Report the values of the sample mean and the sample standard deviation. Be sure
to include appropriate units.
c) Construct a 95% confidence interval for the population mean weld strength. Give
an interpretation for this interval.
d) According to the interval could the population mean weld strength be 17 N?
Explain briefly.
1
2.33
0.98
1.64
1.28
0.67
0.0
-0.67
-1.28
0.9
0.8
0.5
Normal Quantile Plot
3. Corn moisture is a very important characteristic. 72 samples of corn were selected at
random and the moisture (%) was determined for each sample. The data are
summarized in the JMP output below.
0.2
0.1
-1.64
0.02
-2.33
30
20
15
Count
25
10
5
10
11
12
13
14
15
16
17
18
Corn Moisture (%)
Five Number Summary
100.0% maximum
75.0%
quartile
50.0%
median
25.0%
quartile
0.0%
minimum
17.2
15.1
14.5
13.8
11.6
Summary Statistics
Mean
14.5
Std Dev
1.0476
Std Err Mean
0.1235
N
72
a) Describe the shape of the histogram of corn moisture.
b) Report the values of the sample mean and the sample standard deviation. Be sure
to include appropriate units.
c) What is the value of the standard error of the sample mean?
d) Corn with moisture contents above 15% are discounted in the marketplace. Is the
population mean corn moisture 15% or is it something less than 15%? In order to
answer this question you must go through all the steps of a hypothesis test.
2