6.
(07.04 MC)
Students at a local elementary school were randomly selected to
participate in a reading fluency program. The program is designed
to increase their reading fluency. A total of 17 students each took
a pretest before the program and posttest after the program. The
mean differences in the posttest and pretest is 11. The
administration decided that all students in the school would
participate in the program next school year. Let µA denote the mean
score of the posttest and µB denote the mean score of the pretest
for all students in the school. The 90 percent confidence interval
estimate of the difference between the means for all students is
(7, 15). What is an appropriate interpretation of the confidence
interval? (4 points)
For any µ_{A} and µ_{B} with (µ_{A} – µ_{B}) ≥ 9, the sample result is quite likely. 

µ_{A} is greater than µ_{B}, with a probability of 0.90. 

µ_{A} is less than µ_{B}, with a probability of 0.90. 

µ_{A} is approximately 15 and µ_{B} is approximately 7. 

For any µ_{A} and µ_{B} with 7 < (µ_{A} − µ_{B}) < 15, the sample result is quite likely. 
8.
(07.02 LC)
A student working on a report about mathematicians decides to find the 98% confidence interval for the difference in mean age at the time of math discovery for Greek mathematicians versus Egyptian mathematicians. The student finds the ages at the time of math discovery for members of both groups, which include all Greek and Egyptian mathematicians, and uses a calculator to determine the 98% confidence interval based on the t distribution. Why is this procedure not appropriate in this context? (4 points)
The sample sizes for the two groups are not equal. 

Age at the time of math discovery occurs at different intervals in the two countries, so the distribution of ages cannot be the same. 

Ages at the time of math discovery are likely to be skewed rather than bell shaped, so the assumptions for using this confidence interval formula are not valid. 

Age at the time of math discovery is likely to have a few large outliers, so the assumption for using this confidence interval formula is not valid. 

The entire population is measured in both cases, so the actual difference in means can be computed and a confidence interval should not be used. 
9.
(07.02 LC)
The manager of a computer repair shop wants to compare the mean number of motherboard repairs in a week for two repair techniques. Twentyfour technicians from the shop are selected randomly, and each technician is assigned randomly to one of the two techniques. After teaching 12 technicians one technique and 12 technicians the other technique, the manager records the number of motherboard repairs each technician performs in one week. Which of the following is the MOST appropriate inferential statistical test in this situation? (5 points)
A onesample ztest 

A paired ttest 

A twosample ttest 

A chisquare goodnessoffit test 

A onesample ttest 
10.
(07.02 LC)
Randall is conducting a test on bacteria on slices of cheese. He
uses 10 slices of cheese to compare two strains of bacteria. He
applies one strain to the left side of the cheese and one strain to
the right side. He flips a coin to decide which strain goes on the
right side of the cheese. The bacteria holes that appear on each
side are counted and he records them in a table.
Cheese  Number of Holes for Strain 1  Number of Holes for Strain 2 

1 
25 
19 
2 
21 
15 
3 
13 
14 
4 
13 
12 
5 
14 
10 
6 
12 
9 
7 
11 
5 
8 
11 
5 
9 
8 
4 
10 
5 
4 
If Randall is to perform an appropriate ttest to determine if
there is a difference in the mean number of holes per slice of
cheese produced by the two strains, how many degrees of freedom
should he use? (4 points)
7 

8 

9 

10 

18 
11.
(07.05 MC)
In a study of the performance of a tires, the width of tires (in inches) and the life span (in months) for 14 tires were recorded. A regression line was a satisfactory description of the relationship between width of tire and tire life span. The results of the regression analysis are shown in the table.
Variable  Coeff  SE Coeff  t Ratio  pValue 

Constant  7.3985  0.5638  13.12  0.034 
Width of tires  3.9571  0.7382  5.36  0.005 
R squared = 88.5% 
R squared (adj) = 87.9% 
Which of the following should be used to compute a 98% confidence interval for the slope of the regression line? (5 points)
7.3985 ± 2.681(0.5638) 

7.3985 ± 2.624(0.5638) 

3.9571 ± 2.65(0.7382) 

3.9571 ± 2.624(0.7382) 

3.9571 ± 2.681(0.7382) 
12.
(07.05 LC)
The weight (in pounds) and the number of offspring of 23 randomly selected rabbits are compared. Which significance test should be used to determine whether a linear relationship exists between weight and number of offspring, provided the assumptions of the test are met? (4 points)
A twosample ztest 

A twosample ttest 

A ttest for the slope of the regression line 

A chisquare test of independence 

A chisquare goodnessoffit test 
Solution7:
we are
The 90 percent confident that the true difference between the means for all students lies in between 7 and 15
For any µ_{A} and µ_{B} with 7 < (µ_{A} − µ_{B}) < 15, the sample result is quite likely
Solution9:
teaching 12 technicians one technique and 12 technicians the other technique, the manager records the number of motherboard repairs each technician performs in one week.
n1=12 ,n2=12
n1,n2 are independent samples
n1,n2<30
perform t test for difference in means
A twosample ttest
Solution10:
df=n1+n22=10+102=18
ANSWER:
18
Solution11:
slopemargin of errror,slope +margin of error
margin of error=Tc*sd/sqrt(n)
df=142=12
t crit==T.INV.2T(0.02;12)=2.680998=2.681
std error of slope=0.7382
hence MOE=0.7382*2.680998=1.979113
98% confidence interval for the slope of the regression line
slopeMOE,slope+MOE
slope=3.9571
correction option
3.9571 ± 2.681(0.7382)
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