Adding again @HoldMyBeer
The number of zeroes indicate the number of times you can factor out 10 from a number
10 = 2 * 5
25! has a lot of 2s in it:
2,4,6,8,10 alone give 8 2s
So 5 is the limiting factor, the number of 5s in 25!:
1 (5) + 1(10)+ 1 (15) + 1(20) + 2(25) = 6
Number of 10s = 6
So number of zeroes at the end of 25! = 6
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