A car-rental company is interested in the amount of time its vehicles are out of
ID: 3296252 • Letter: A
Question
A car-rental company is interested in the amount of time its vehicles are out of operation for repair work. State all assumptions and find a 98 % confidence interval for the mean number of days in a year that all vehicles in the company's fleet are out of operation if a random sample of 10 cars showed the following number of days that each had been inoperative.
15
17
22
19
13
9
25
11
16
5
State all assumptions. Select all the assumptions below.
A.
The sample comes from a normal population
B.
The sample size is at least 30
C.
The variance is less than the mean
D.
It is a random sample
Find a
98
%
confidence interval for the population mean.
The
98
%
confidence interval is from a lower limit of
________
to an upper limit of
___________
.
(Round to two decimal places as needed.)
Explanation / Answer
Assumption:
D. It is a random sample
mean = 15.2 , std.deviation = 6.015, n =10
t value at 98% CI = 2.821
CI = mean +/- t * ( s/sqrt(n))
= 15.2 +/- 2.821 * ( 6.015/sqrt(10))
= (9.8342, 20.5659)
Lower limit = 9.8342
Upper limit = 20.5659
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