A sample of 150 calls to a customer help line during one week found that callers were kept waiting on average for 16 minutes with s = 8.
(a) Find the margin of error for this result if we use a 95% confidence interval for the length of time all customers during this period are kept waiting.
(b) Interpret for management the margin of error.
(c) If we only need to be 90% confident, does the confidence interval become wider or narrower?
(d) Find the 90% confidence interval.