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 those numbers (day 1 --> 15 sold, .... day 24 --> 32 sold)

When calculating Standard deviation in excel, do you use Standard deviation sample (STDEV.S) or Standard deviation population (STDEV.P)?