Confidence Intervals

Question

Assume the age of school students is normally distributed. A simple random sample of 24 school students had an average age of 27.3 years. Use this information and a population standard deviation of 5.6 to find a :

 

1.) 90% confidence interval estimate for the population variance

 

 

2.) 90% confidence interval estimate for the population standard deviation

Answer 1

1) we are going to take the mean and add and subtract the standard deviation * the 90% z-score:

mean +/- z* x standard deviation

27.3 +/- 1.645 * 5.6 = [18.088,36.512]

2) there is no such thing as a confidence interval for the population standard deviation. For a 90% confidence interval you go 1.645 standard deviations out from the sample mean to get a confidence interval.

Hope this helps and let me know if you have anymore questions.