<PRE><B>Question 999315</B>
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i have invited nine people to a party. They all shake hands with me, and each pair shake hands. how many hand shakes are there?
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The answer is &amp;nbsp;{{{(n*(n-1))/2}}}. &amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;({{{C[n]^2}}}, &amp;nbsp;if you know what does it mean).


If &amp;nbsp;n = 9+1 = 10, &amp;nbsp;then the number of hand shakes is {{{(10*9)/2}}} = 45.


This is very standard problem on combinations.





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