In: Statistics and Probability
With economical concerns being so great, many people are no longer purchasing new vehicles, but are instead keeping their vehicles for a longer period of time, until they no longer work. The Amer-ican Automobile Association is interested in estimating the average age of vehicles for Americans. A random sample of thirty-five Americans was obtained. The average age of their vehicles was 6.2 years with standard deviation 1.2. Estimate with 99% confidence the average age of vehicles for Americans
Solution :
Given that,
Point estimate = sample mean =
= 6.2
Population standard deviation =
= 1.2
Sample size = n =35
At 99% confidence level the z is ,
= 1 - 99% = 1 - 0.99 = 0.01
/ 2 = 0.01 / 2 = 0.005
Z/2 = Z0.005 = 2.576
Margin of error = E = Z/2* ( /n)
= 2.576* ( 1.2/ 35)
= 0.5225
At 99% confidence interval estimate of the population mean is,
- E < < + E
6.2 - 0.5225< <6.2 + 0.5225
5.6775< < 6.7225
(5.6775 , 6.7225)