How many numbers of at most three different digits can be formed the integers 5,6,7,8,9?​

Question: How many numbers of at most three different digits can be formed the integers 5,6,7,8,9?

Solution: Total Digits = n = 5 {5,6,7,8,9}
Total number of single digit numbers = n = 5
Total number of two digit numbers = 5P2 = 5 * 4 = 20
Total Number of three digit numbers = 5P3 = 5*4*3 = 60
Thus, Total numbers of at most three different digits that can be formed = 5 + 20 + 60 = 85