Answer to Question #19901 in Statistics and Probability for john

Question

In a recent sample of 84 used cars sales cost, the sample mean was $6425 with a standard deviation of $3156. Assume the underlying distribution is approximately normal. Construct a 95 % confidence interval for the population average cost of a used car

Answer 1

to find confidence interval we need
standard deviation/ sqrt (sample size) = 3156/sqrt(84) = 344,3
finding the coefficient from t-distr. table and multiplying on previous number we get
344.3*(1.96) = 674.8
hence, confidence interval is $6425 +- $674.8