Hi all, I know what factorials are, obviously, and permutations and combinations, but what I Don't know is, given a problem with factorials in it, is there a general format for solving? For instance, an old AMC 10 problem: 10B-#11. What is the tens digit in the sum 7! + 8! + 9! + . . . + 2006! ? (A) 1 (B) 3 (C) 4 (D) 6 (E) 9 How would one go about solving this? All help appreciated!