Statistics

[kirchi]

An ambulance agency claims that the standard deviation of the length of service times is 5
minutes. Investigator suspects that this claim is wrong. She takes a random sample of 20
services and finds the standard deviation as 6 minutes. Assume that the service time of the
ambulance follows normal distribution.
i) What is the probability that the standard deviation of the length of service times is more
than and equal to 5 minutes.
ii) Find the 95% confidence interval for the standard deviation of the length of service times.
iii) Test, at  = 0.01, is there enough evidence to reject the agency’s claim?

[Reeza]

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@kirchi wrote:

An ambulance agency claims that the standard deviation of the length of service times is 5
minutes. Investigator suspects that this claim is wrong. She takes a random sample of 20
services and finds the standard deviation as 6 minutes. Assume that the service time of the
ambulance follows normal distribution.
i) What is the probability that the standard deviation of the length of service times is more
than and equal to 5 minutes.
ii) Find the 95% confidence interval for the standard deviation of the length of service times.
iii) Test, at  = 0.01, is there enough evidence to reject the agency’s claim?

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PROC TTEST. 

[kirchi]

Please! Can you help me more?

I have sample standard deviation or standard error, population standard deviation and sample size. i don't know, how to use t-test?

[Reeza]

See the videos here and check the documentation for proc TTEST under examples. 

http://support.sas.com/training/tutorial/