The marketing director of a large department store in Metro Manila wants to estimate the average number of customers who enter the store every five minutes. She randomly selects five-minute intervals and counts the number of arrivals at the store. She obtains the figures: 31,37,42,49,52,54,65.68. Find the mean of this sample. 49.8 Find the standard deviation of this sample. 12.9 Give the t-value for a 95% confidence coefficient, assuming a normal distribution. 2.365 Give a 95% confidence interval for the number of arrivals. (39.0, 60.5) Suppose the computed 95% confidence interval is (39, 60), which of the below interpretation is correct. [Select] [Select] there is a 95% probability that the true mean is 39. If we get many additional random samples and from each compute a 95% confidence intervals, approximately 95% of these intervals would contain the true average arrivals. All of the above are true. 95% of values sampled are between 39 and 60.