The integer a ends in a string of n zeros. If

what is n?

Solution:

so a = 100!.  The number of zeros at the end of 100! is the same as the number of 5s in its prime factorization. There are 20 factors of 5 in the first 100 integers, but 4 of them are also factors of 25, yielding 24 factors of 5 in all.