b. What percent of customers at the drive-through lane will take between 1 to 3 minutes to service?
Part B1. A simple random sample of 50 customers is selected from an account receivable portfolio and the sample mean account balance is $1000. The population standard deviation s is known to be $200. (8 points) a. Construct a 95% confidence interval for the mean account balance of the popula-tion.
b. What is the margin of error for estimating the mean account balance at the 95% confidence level?
c. Construct a 95% confidence interval for the mean account balance of the popula-tion if the samples mean account balance is obtained from a random sample of 100 instead of 50.
Assignment #3
May 19
d. Based on the results from a. and c., what can you say about the effect of a larger sample size on the length of the confidence interval at the same confidence level?
2. A simple random sample of 50 calls is monitored at an in-bound call center and the average length of the calls is 6 minutes. The population standard deviation is unknown. Instead the sample standard deviation s is also calculated from the sam-ple and is found to be 4 minutes. (6 points) a. Construct a 99% confidence interval (using the t-distribution) for the average length of inbound calls.
