1. A survey involving a random sample of customers of the supermarket which the checkout times are between 3 to 6 minutes (180 to 720 seconds) is

1.     A survey involving a random sample of customers of the supermarket which the checkout times are between 3 to 6 minutes (180 to 720 seconds) is planned and the first order of business is to decide on an appropriate sample size. The 95% level of confidence will be used.

a.     What is the planning value for the population standard deviation to be used in the sample size formula for estimating the population mean check-out time?

b.     How large should the sample size be if the desired margin of error is 25 seconds?