2006 AMC 10B Problems/Problem 11

From AoPSWiki

Problem

What is the tens digit in the sum

Solution

Since is divisible by , any factorial greater than is also divisible by . The last two digits of all factorials greater than are , so the last two digits of is .

So all that is needed is the tens digit of the sum

So the tens digit is

See Also

• 2006 AMC 10B Problems

• Previous Problem

• Next Problem