Question 1172639
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For nice description of the  Birthday  Problem,  see this  Wikipedia article


<A HREF=https://en.wikipedia.org/wiki/Birthday_problem>https://en.wikipedia.org/wiki/Birthday_problem</A>


https://en.wikipedia.org/wiki/Birthday_problem




For the &nbsp;99.9% &nbsp;probability, &nbsp;this article gives the answer &nbsp;70 &nbsp;people in the group.