Download Chapter 11 Problems

Chapter 11
1.
Problems
The Andersons Super Dollar had two grocery stores in Erie, Pennsylvania. The mean
time customers wait in the checkout line at the Byrne Road store is 3.7 minute with a
standard deviation of .8 minutes, for a sample of 40 customers. The mean waiting time
for the I-90 store is 3.5 minutes with a standard deviation of .7 minutes for a sample of 45
customers. At the .05 significance level can we conclude there is a difference in the
waiting time for the two stores?
H 0 :  B   90
H 1 :  B   90
Reject H 0 if z  1.96 or z  1.96.
z
3.7 - 3.5
 1.22
.8 2 .7 2

40 45
Do not reject H 0 . We cannot conlude there is a difference in the mean
waiting time for the two stores.
2.
A sample of 200 Lion Store charge customers 50 years or older showed that 20 did not
pay their entire balance at the end of the month. A sample of 300 customers under 30
showed that 50 did not pay their entire balance at the end of the month. At the .02
significance level can we conclude that a larger percent of the younger customers do not
pay their entire balance at the end of the month?
H0 :O  Y
H1 :  O   Y
Reject H 0 if z  -2.06.
20  50
20
50
 .14 , pO 
 .10 , pY 
.1667
200  300
200
300
.10  .1667
z
 2.11
.14 (. 86 ) .14 (. 86 )

300
200
Reject H 0 . The percent of those not paying the entire amount is less for those over 50.
pc 
3. The mean high temperature for 12 days in July in Detroit, Michigan was 88 degrees with
a standard deviation of 4 degrees. The mean high temperature in Hilton Head, South
Carolina for 8 July days was 91 degrees with a standard deviation of 3 degrees. At the
.05 significance level, can we conclude that it is warmer in Hilton Head?
1
H0 : H  D
H1 :  H   D
Reject H 0 if t  1.734.
(12 - 1)4 2  (8  1)32
 13 .2778
12  8  2
91  88
t
 1.804
1 1 
13 .2778   
 8 12 
Reject H 0 . The mean tempe rature is warmer in Hilton Head.
s 2p 
4.
An egg farmer wanted to determine if increasing the time the lights were on in his hen
house would increase egg production. For a sample of eight chickens he determined their
production before and after increasing the amount of time the lights were on. The data
are reported below. At the .01 significance level, has there been an increase in
production?
Hen
Before
After
1
10
7
2
8
5
3
5
6
4
2
8
5
3
8
6
7
8
7
3
10
8
3
2
H 0 : d  0
H1 :  d  0
Reject H 0 if t  2.998.
13 2
8  3.962
sd 
8 1
1.625
t
 1.160
3.962 8
131 
d 
13
 1.625
8
Do not reject H 0 . There is no increase in the egg production with the lights on.
2