Problem: We use 8 digits 0, 1, 2, 3, 4, 5, 6, 7 to form all 5-digit natural numbers consisting of distinct digits. Find the sum of all numbers that can be formed.
Sum the numbers: 1 + 2 + 3 + 4 + 5 + 6 + 7 =36
Because 36 when 0 = 36-1
So = 35
So take the largest number = 35: 7 = 5