QUESTION 15 A random sample of 49 statistics examinations was taken. The average
ID: 3358903 • Letter: Q
Question
QUESTION 15
A random sample of 49 statistics examinations was taken. The average score, in the sample, was 85 with a variance of 12.25. The 95% confidence interval for the average examination score of the population of the examinations is (rounding to the nearest integer)
a.
81.00 to 89.00
b.
82.00 to 88.00
c.
83.00 to 87.00
d.
84.00 to 86.00
QUESTION 16
The sample size needed to provide a margin of error of 2 or less with a .90 probability when the population standard deviation equals 10 is
a.
97
b.
96
c.
68
d.
67
QUESTION 17
In a random sample of 144 observations, = 0.4. The 95% confidence interval for P is
a.
0.28 to 0.52
b.
0.30 to 0.50
c.
0.32 to 0.48
d.
0.34 to 0.56
QUESTION 18
The manager of a department store wants to determine what proportion of people who enter the store use the store's credit cards for their purchases. What size sample should he take so that at 95% confidence the error will not be more than 4%?
a.
267
b.
423
c.
601
d.
Since the is not given, there is no answer to this question.
QUESTION 19
In order to estimate the average electric usage per month, a sample of 225 houses was selected, and their electric usage determined. Assume a population standard deviation of 390-kilowatt hours. Determine the standard error of the mean.
a.
1.73
b.
3.01
c.
25
d.
26
QUESTION 20
A random sample of 100 credit sales in a department store showed an average sale of $90.00. From past data, it is known that the standard deviation of the population is $30.00. What is the 90% confidence interval of the population mean
a.
84.00 to 96.00
b.
85.06 to 94.94
c.
84.12 to 95.88
d.
82.27 to 97.73
Explanation / Answer
Mean is 85 and standard deviation s is 12.25, the standard error is s/sqrt(N)=12.25/sqrt(49)=1.75
for 95% confidence, the z value is 1.96
thus lower limit is mean-s*z=85-1.75*1.96 =81.57 or 82
upper limit is mean+s*z=85+1.75*1.96=88.43 or 88
thus answer is B
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