Find the last two digits of the following sum: 5! + 6! + 7! + 8! + 9! + 10! + ... + 100!
120 + 720 + 5040 + 40320 + 362880 + 3628800......
which is 20 + 20 + 40 + 20 + 80 + 00 +00 +00.......,
which means last two digit is: 80
+191 
