Question 550226
51<P>
201! - 200! = 201*200! - 200! = 200*200!<P>
To find the number of trailing zeros in any n! determine the number of times it is divisible by all smaller powers of 5.  <P>
The reason it works is that zeros happen whenever 10 is a factor, and 5 and 2 are factors of 10.  Find the number of 5's that factor into the n! n, also the number of 5x5's and 5x5x5's etc.<P>
Ignore remainders<P>
200/5 = 40 + 200/25=8 + 200/125=1 = 49.<P>
But this n! is multiplied by another number.  Each of the zeros at the end of 200 will create a trailing 0.  So it's 49+2 = 51.<P>

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