Expert: Richard J. Raridon - 6/7/2010

Question
Five-digit sum. Find the sum of all five-digit numbers that are formed by using the digits 1, 2, 3, 4, and 5 once and only once.

Answer
Okay, let's reason it out.  If you look at only 3 digits, you have 321,312,231,213,123,132.  If you add those up you will see that the sum of each column is 12 and therefore the total sum is
1332.  For 5 digits you have 120 numbers and in each column you have 1+2+3+4+5 twenty times for a total of 300.  So if you add up all the columns you should get 333300.