Construct a 95% confidence interval for the mean time taken to mail products for all orders received at the office

Question

A computer company sells computers and computer parts by mail. The company assures its customers that products are mailed as soon as possible after an order is placed with the company. A sample of 36 recent orders showed that the mean time taken to mail products for these orders was 70 hours. Suppose the population standard deviation is 16 hours and the population is normal. Construct a 95% confidence interval for the mean time taken to mail products for all orders received at the office

Answer 1

   mean +or- 1.96*stdev/sqrt(N)

 

   mean=70, stdev=16, N=36 ,  and 1.96 because of 95% confidence level per normal table.

 

 

    70 + 1.96*16/sqrt(36) = 75.226

 

   70 - 1.96*16/sqrt(36) = 64.773

 

(64.773 , 75.226)