Given a data set {5, 2, 9, 3, 5, 8, 5, 7, 2}, find the mode of the set.

Step 1 ：First, list the data set in ascending order: {2, 2, 3, 5, 5, 5, 7, 8, 9}.

Step 2 ：Then, count the frequency of each number: 2 appears 2 times, 3 appears 1 time, 5 appears 3 times, 7 appears 1 time, 8 appears 1 time, and 9 appears 1 time.

Step 3 ：The mode is the number that appears most frequently. In this case, the number 5 appears 3 times, which is more than any other number.