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jmc

number theory senior

Problem

The number 236! ends in how many zeros when expressed as an integer?
Solution
To find the number of terminal zeros, we must find the number of products in . Since there are more factors of 2 than factors of 5, we can get our answer by finding the largest power of 5 that divides . Every multiple of 5 less than 236 gives a factor of 5, each multiple of 25 gives an additional factor of 5, and each multiple of 125 gives a third factor of 5. Therefore, the number of factors of 5 in is . The highest power of 5 that divides is so ends in zeros.
Final answer
57