In: Statistics and Probability
A researcher for a car insurance company wishes to estimate the mean annual premium that men aged 20-24 years pay for their car insurance. A random sample of 50 men aged 20-24 years shows a mean of $711. Assume that the distribution of annual premiums has a standard deviation of $185.
a) Find a 94% confidence interval for the mean annual premium for all men aged 20-24 years.
b) What is the error of the estimate?
c) Find the 99% confidence interval for the mean annual premium for all men aged 20-24 years. Which confidence interval is wider?
d) How large a sample is necessary if we wish to be 94% confident that the sample mean will be within $20 of the true mean?
By comparing 94 % and 99 % confidence interval we know that 99% confidence interval is wider.
d) C = 0.94 , = 185 , E = 20
We have asked to find the sample size n.
We know that-
Sample size n = [(Z0.94 * ) / E]2
= [ (1.88 * 185) / 20 ]2
= 302.67
303 (Rounded to the next integer)
Hence the required sample size n = 303