2007 Cyprus MO/Lyceum/Problem 28
Revision as of 14:28, 6 May 2007 by I_like_pie (talk | contribs)
Problem
The product of 
is an integer number whose last digits are zeros. How many zeros are there?
Solution
The number of zeros at the end of a number is determined by the number of 2's and 5's in its prime factorization.
There are 12 2's and 19 5's. Each pair adds a zero, but any extras don't count (in this case, the 7 extra 5's).
