Statistics 104 – Homework 12
Due Tuesday, December 10, 2013
Homework is due on the due date at the end of the lecture.
Reading:
November 21 – December 5
December 10 – December 12
Sections 8.3 and 9.3
Sections 10.2 and 10.4
Assignment:
1. Complete the following problems from the text: 8.27, 8.29, 9.29, and 9.31.
8.27 Females’ ideal number of children.
8.29 Using t-table.
9.29 Effect of n.
9.31 Men at work.
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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.
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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.
Corn Moisture (%)
Five Number Summary
Summary Statistics
100.0% maximum
17.2 Mean
14.5
75.0%
quartile
15.1 Std Dev
1.0476
50.0%
median
14.5 Std Err Mean
0.1235
25.0%
quartile
13.8 N
72
0.0%
minimum
11.6
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.
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c) What is the value of the standard error of the sample mean?
d) Corn with moisture contents at 15% or above does not get as good a price 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.
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