A small umbrella shop is planning to analyze their sales over the last 24 winter days. This company wants to know how many umbrellas can be expected to sell on a daily basis during winter. Based on past studies on the subject, the shop knows the number of umbrellas sold per day is well approximated by a normal distribution. The number of umbrella sales were recorded for the last 24 days and you are given that data (day 1 --> 15 sold ..... day 24 --> 32 sold).

To find standard deviation in excel, do you use standard deviation sample forumula (STDEV.S) or standard deviation population (STDEV.P) forumula?