The list below shows the length in days of each of the space shuttle Atlantis's first 31 missions.

4, 7, 4, 4, 5, 4, 5, 6, 9, 7, 9, 8, 11, 10, 8, 9, 10, 10, 9, 11, 10, 12, 13, 13, 11, 11, 12, 14, 13, 13, 11

Calculate the following to help analyze the data set. If the answer is not a whole number, use a decimal and round to the nearest tenth.