Math 158 Fall 2011
Name:
Due 9/19 at 10:20 am
_____________________________________________
You’ll need Minitab. It’s available as a download for pc; it also is installed on most campus pcs.
You may consult with others on how to get the required information in both Minitab and Excel. Each
person must hand in this sheet, and your work must represent your ability to perform the tasks exactly as
described on the sheet that you submit.
Credit Card Use
A credit card company wants to see how much customers in a particular segment of the market use their credit
card. They have provided you with data on the amount spent by 484 selected customers during a 3-month period,
and have asked you to summarize the expenditures. This exercise will take you through some of the first steps in
an organized data analysis.
The data are found among the files in the instructor’s Shared Folder in LakerApps: Credit Card Use. The best
thing to do with this file is to first download it as Excel to your computer. Open the file in Excel, then copy and
paste the data into Minitab.
Obtain a histogram of the data.1. (You can improve upon the histogram by double clicking the x-axis, clicking the
Binning tab, and selecting cutpoints rather than midpoints.) Also obtain a boxplot.2 What shape is this
distribution?
______________________________________
Mode = __________
Obtain descriptive statistics for the data.3
Mean = __________
Median = __________
Standard deviation = __________
Range = __________
IQR = __________
Compute Range / SD (SD stands for “Standard Deviation”) using the values Minitab provides. (Ignore SEMEAN
– we don’t know what that is . . . yet.) When you have the value to the nearest 0.1, write it in the blank in the
following sentence:
The range is _______ times the standard deviation. (Nearest 0.01, please.)
Move to Excel. We’ll use Excel to obtain some percentiles.
Your unsorted data should be in the array A2:A485. Cell A1 is the variable description “Average Monthly
Spending.” Don’t forget to sort before starting!
1
Instructions are found on page 57 of the text, as well as in any number of places online.
Page 125, etc.
3
Page 93, etc.
2
If you do not have Excel 2010 or Excel mac:2011: Use the functions PERCENTRANK and PERCENTILE
(without the .EXC). The inputs work exactly the same as for PERCENTRANK.EXC and PERCENTILE.EXC
respectively.
Which version of Excel are you using? (Circle exactly one. Failing to do so gives you 0 for the assignment.)
Excel 2010 for pc
Excel mac:2011
Some other version
Display all $ amounts to the nearest penny = $0.01.
Determine the 75th percentile in Excel. Compare this to Minitab’s Q3. The two are very close.
Now determine the 40th and 60th percentiles.
The 40th percentile is $ ____________ .
The 80th percentile is $ ____________ .
Find the percentile rank of the amount $209.40. Remember: Excel will output a fraction – multiply it by 100 to
get a percent. You can check this against the value for Q1 (the 25th percentile) provided by Minitab’s descriptive
statistics. Again, the two are very close.
Determine the percentile ranks for amounts of $15, $150, $1500 and $4500. Percentages between 1% and 10%
and those between 90% and 99% should be rounded to no more than the nearest 0.1% (not the nearest 1%).
Percentages between 0.1 and 1.0% and between 99.0 and 99.9% should be rounded to no more than the nearest
0.01%.
The percentile rank of $15 is __________ .
nearest 0.1%
The percentile rank of $150 is __________ .
nearest 1%
The percentile rank of $1500 is __________ .
nearest 1%
The percentile rank of $4500 is __________ .
nearest 0.01%
Circle the letters corresponding to situations where percentiles and percentile ranks would be a useful
way to summarize data.
[circle – or don’t – these]
A
B
C
D
E
A. Data on the number of cars owned by
households.
B. Data on the company that people have their
primary personal cell phone contract with.
C. Data on the first digit of share prices for
companies listed on the New York Stock
Exchange.
D. Data on the size (in square feet) of houses in
Oswego.
E. Data on the amounts for grocery bills for shoppers.