If 11 persons meet at a reunion and each person shakes hands exactly once with each of the others, what is the total number of handshakes? Answers:
A) 10•9•8•7•6•5•4•3•2•1
B) 10•10
C) 55
D) 45
E) 36
We got #11 people who shake each other's hands once ==&gt; a pair of 2   11!/9!2! = 11*10 / 2*1= 
<gadget id="calculator">11*10 / 2*1</gadget>
<output>55</output>
55.   Hence answer 55.
<result>C</result>
If 11 persons meet at a reunion and each person shakes hands exactly once with each of the others, what is the total number of handshakes?