number theory - Factorial related problems

How many zeros are there in $25!$ ?
My answer was $6$. But i solved it by finding how many numbers are divisible by $5$ and $2$.here i was told to find out the zeros at the last end.
But what is the method which is more accurate and can find out the number of zeros in eg $1000!$ or $10000!$ in the following cases:
1.Just at the last end
2.In the number altogether
Or even the general method of finding the number of zeros in n! ?