Suppose that a sample of customers per hour were randomly taken from a store and that the

Question:

Suppose that a sample of customers per hour were randomly taken from a store and that the sample standard deviation of the number of customers per hour was 2.4 are based on this information. Assume that the number of customers per hour is normally distributed.
If the sample size were 15 instead of 10, show why the 95% confidence interval would be narrower.