PSL4#74

8 1 digit numbers, leaves 7 each of the digits 1-8

81-87 uses all the 8s and leaves 6 each of 1-7

71-76 uses all the 7s and leaves 5 each of 1-6

61-65 leaves 4 each of 1-5

51-54

41-43

31-32

21

 

8 + 7 + 6 + 5 + 4 + 3 + 2 + 1 = (8)(9)/2 = 36