Number of even numbers in the set of {1...100} is 50
Number of numbers which have factors of 5 in the set {1...100} is 20 (100/5).
However numbers 25,50,75,100 have two 5's as factors.
Zeroes at the end of 100! are generated when  5 is multiplied by 2.
There are 20+4=24 5's which are factors in the set {1...100}.

There are 24 zeroes at the end of 100!
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