Question 248731
number of zeros = number of factors of 10 = number of factors of 5 (Factors of 5 are less common than factors of 2.)


Keep dividing the result by 5 until you can't.


1000/5 = 200
200/5 = 40
40/5 = 8
8/5 = 1.6 --> 1


1000! ends with 200 + 40 + 8 + 1 = 249 zeros.