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