Math Is Fun Forum

wicknapp

Member

Registered: 2006-11-28

Posts: 1

sum the digit in 100!

I am solving ten problems that all are suppose to result in a single digit answer.  One of the problems is stated as such

"n! means n × (n-1) × (n-2) ... × 3 × 2 × 1
Find the sum of the digits in the number 100!
Then:
subtract 3 from this value to get your answer"

I computed 100! to be the 158 digit numer 9332262..... and the sum of the digits 9+3+3+.... to be 648.  So  648-3=645.  As I said, this is suppose to end up a single digit.  I have asked the author the same question, but he would not surrender any clues.  Am I missing some kind of riddle/brainteaser in how the problem is stated?

Thanks.

Ricky

Moderator

Registered: 2005-12-04

Posts: 3,791

Re: sum the digit in 100!

The answer is -2.  Just think of someone really excited asking you the question.

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"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."