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```							252hwkadd 12/01/03         (Open this document in 'Print Layout' view!)               Roger Even Bove

PROBLEMS THAT APPEAR IN THE 9TH EDITION BUT NOT THE 8TH (and some from the 8th or other places. )

9.40 Suppose that in a one-tail hypothesis test where you reject H 0 only in the lower tail, you compute the value of the test statistic
z as 1.38, what is the p-value?

9.41 In Problem 9.40, what would be your statistical decision if you tested the null hypothesis at the 0.01 level of significance?

9.66 In a national poll of 811 personal computer owners, Peter D. Hart Research Associates found that 44% (357) of the PC owners
ranked sharing their credit card information as the number one concern in on-line shopping. The survey also indicated that 72% (584)
of PC owners would purchase a more secure computer if available. When given the actual dollar amount the added security would cost,
57% (462) indicated that they would pay an extra \$75 for a new PC delivering a more secure on-line experience.
a. Test the null hypothesis that 50% of all PC owners in the United States rank sharing their credit card information as the
number one concern in on-line shopping versus the alternative that the percentage is not equal to 50%   .05
b. Compute the p-value in(a) and interpret its meaning.
c. At the .05 level of significance, is there evidence that more than half of all PC owners in the United States would pay an
extra \$75 for a new PC delivering as more secure on-line experience?
d. Compute the p-value in(c) and interpret its meaning.
e. At the .05 level of significance, is there evidence that more than 55% of all PC owners in the United States would pay an
extra \$75 for a new PC delivering as more secure on-line experience?
f. Compute the p-value in(e) and interpret its meaning.

9.67 To handle the increased necessity of storing and organizing huge amounts of data, many companies are making large
expenditures for increased data-storage expenditures. The slowdown in the US economy, however, has many companies delaying data
storage expenditures. In July 2001, it was reported that 38% of the companies surveyed have delayed expenditures on storage
deployments because of the economic slowdown. The sample size of this survey was not disclosed.
a. Suppose that the above results were based on the responses of 50 companies. Is there evidence at the .01 level of
significance that less than half of all companies are delaying data-storage expenditures?
b. Compute the p-value in(a) and interpret its meaning.
c. Suppose that the above results were based on the responses of 100 companies. Is there evidence at the .01 level of
significance that less than half of all companies are delaying data-storage expenditures?
d. Compute the p-value in(c) and interpret its meaning.
e. Compare your answers in (a) and (b) with your answers to (c) and (d). Explain the effect that sample size has on statistical
significance.
f. What ethical issues are raised when one fails to report the sample size used in a survey?

10.32 HomeGrocer.com vs. local Seattle supermarkets.

Products                                                                HomeGrocer        Supermarkets

1    Tide High Efficiency, 64 oz.                                       6.99                  6.99
2    Oreo Cookies, 20 oz.                                               3.29                  3.49
3    Formula 409 Cleaner, 22 oz.                                        2.59                  2.69
4    Pampers Newborn Diapers, 40 count                                 10.79                 10.99
5    Coke Classic, dozen 12 oz. Cans                                    3.99                  3.59
6    Colgate Total Toothpaste, 7.8 oz.                                  3.49                  3.49
7    Tropicana Orange Juice, 64 oz.                                     3.59                  3.49
8    Cheerrios Whole Grain Cereal, 20 oz.                               4.29                  3.99

a. At the 0.05 level, is there evidence of a difference in the average price for products purchased from the two vendors?
b. Compute the p-value in(a) and interpret its meaning.
c. Set up a 95% confidence interval estimate of the difference in the average price for products purchased from the two
vendors?
d. Compare the results in (a) and (c).
12.7 Of 56 white workers terminated, 29 claimed bias. Of 407 black workers terminated, 126 claimed bias.
a. At the 5% significance level, is there evidence that white workers are more likely to claim bias than black workers?
b. Find and interpret the p-value in a.

12.8 500 African Americans and 500 whites (all with incomes above \$50000) were surveyed with the result that 74% of the African-
Americans and 84% of the whites owned stocks.
a. At the 5% significance level, is there a significant difference between the proportion of African Americans and the
proportion of whites who own stocks?
b. Find and interpret the p-value in a.
c. Set up a 95% confidence interval for the difference between the two proportions.

D6a Given: H 0 :  1   2 , H 1 :  1   2 , n1  16, n 2  21, s1  100 and s 2  400 . Test the hypotheses using only right tail
2     2           2     2                       2             2

tests.   .05 .

12.23 The results of a Gallup phone survey appear below. Consumers were asked if they objected to having their medical records
shared with different types of organizations. Results follow.
O      Ins Cos Pharm Research
Yes  820               590      670 
                                
No  180
                410       330  

a) Is the proportion of people who object different for different institutions?   .05.
b) If appropriate, use the Marascuilo procedure to determine which organizations are different. Discuss.

12.49 The manager of a computer network has the following data on service interruptions per day over the last 500 days. Does it
follow a Poisson distribution?   .01
Interruptions Number
per day     of days
0         160
1         175
2          86
3          41
4          18
5          12
6           8
Total       500

12.52 A random sample of 500 car batteries revealed the following distribution of battery life in years. If x  2.80 and s  0.97,
does it follow a Normal distribution?   .05
Life    Frequency
0  under 1     12
1  under 2     94
2  under 3    170
3  under 4    188
4  under 5     28
5  under 6      8
Total       500
14.4 Computer Output.

————— 11/20/2003 11:23:07 PM ————————————————————

Welcome to Minitab, press F1 for help.
MTB > Retrieve "C:\Berenson\Data_Files-9th\Minitab\Warecost.MTW".
2
Retrieving worksheet from file: C:\Berenson\Data_Files-9th\Minitab\Warecost.MTW
# Worksheet was saved on Mon Apr 27 1998

Results for: Warecost.MTW

MTB > Regress c1 2 c2 c3;
SUBC>   Constant;
SUBC>   VIF;
SUBC>   Brief 3.

Regression Analysis: DistCost versus Sales, Orders                Minitab regression Output.

The regression equation is
DistCost = - 2.73 + 0.0471 Sales + 0.0119 Orders

Predictor            Coef         SE Coef             T       P         VIF
Constant           -2.728           6.158         -0.44   0.662
Sales             0.04711         0.02033          2.32   0.031         2.8
Orders           0.011947        0.002249          5.31   0.000         2.8

S = 4.766             R-Sq = 87.6%          R-Sq(adj) = 86.4%

Analysis of Variance

Source                 DF             SS             MS        F          P
Regression              2         3368.1         1684.0    74.13      0.000
Residual Error         21          477.0           22.7
Total                  23         3845.1

Source           DF          Seq SS
Sales             1          2726.8
Orders            1           641.3

Obs          Sales     DistCost            Fit        SE Fit    Residual      St Resid
1            386       52.950         63.425         1.332     -10.475         -2.29R
2            446       71.660         63.755         1.511       7.905          1.75
3            512       85.580         84.820         1.656       0.760          0.17
4            401       63.690         67.082         1.332      -3.392         -0.74
5            457       72.810         70.127         0.999       2.683          0.58
6            458       68.440         67.796         1.193       0.644          0.14
7            301       52.460         49.839         2.134       2.621          0.62
8            484       70.770         77.528         1.139      -6.758         -1.46
9            517       82.030         84.196         1.525      -2.166         -0.48
10            503       74.390         77.503         1.126      -3.113         -0.67
11            535       70.840         75.199         1.838      -4.359         -0.99
12            353       54.080         48.800         2.277       5.280          1.26
13            372       62.980         62.311         1.483       0.669          0.15
14            328       72.300         65.626         2.847       6.674          1.75
15            408       58.990         63.852         1.152      -4.862         -1.05
16            491       79.380         75.145         1.069       4.235          0.91
17            527       94.440         88.789         2.004       5.651          1.31
18            444       59.740         59.407         2.155       0.333          0.08
19            623       90.500         87.302         2.535       3.198          0.79
20            596       93.240         93.867         2.097      -0.627         -0.15
21            463       69.330         70.087         1.049      -0.757         -0.16
22            389       53.710         59.898         1.349      -6.188         -1.35
23            547       89.180         87.401         1.657       1.779          0.40
24            415       66.800         66.535         1.107       0.265          0.06

R denotes an observation with a large standardized residual

MTB > Print c1-c3

Data Display                Original Data

Row      DistCost    Sales    Orders

1      52.95      386      4015
2      71.66      446      3806
3
3       85.58       512       5309
4       63.69       401       4262
5       72.81       457       4296
6       68.44       458       4097
7       52.46       301       3213
8       70.77       484       4809
9       82.03       517       5237
10       74.39       503       4732
11       70.84       535       4413
12       54.08       353       2921
13       62.98       372       3977
14       72.30       328       4428
15       58.99       408       3964
16       79.38       491       4582
17       94.44       527       5582
18       59.74       444       3450
19       90.50       623       5079
20       93.24       596       5735
21       69.33       463       4269
22       53.71       389       3708
23       89.18       547       5387
24       66.80       415       4161

MTB > Save "C:\Documents and Settings\RBOVE.WCUPANET\My Documents\Drive D\MINITAB\Warecost.MTW";
SUBC>    Replace.
Saving file as: C:\Documents and Settings\RBOVE.WCUPANET\My Documents\Drive D\MINITAB\Warecost.MTW
MTB > Stop.

13.36 Suppose that you are testing the null hypothesis that there is no relationship between x and y . Assume n  20 and that
SSR  60 and SSE  40 .
a. What is the value of the F test statistic?
b. At the 5% significance level what is the critical value of F?
c. Based on the answers to a) and b) what statistical decision should be made?
d. Calculate the correlation coefficient from R 2 by assuming that the slope b1 is negative.
e. At the 5% significance level, is there significant correlation between x and y ?

4

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