What is the units digit of 1! + 2! + 3! + 4! + ... + 50!
Just add the first 4 or 5 numbers, because after that they all end in zeros:
1! + 2! + 3! + 4! + 5! =
1 + 2 + 6 + 24 + 120 =153 - so, units digit is 3.