help

 

A group of 12 people attend a meeting. Every pair of people shook hands with each other. How many handshakes were there?    

 

I'm not certain of this, so wait for somebody else to chime in.  But you could start thinking about the following.  

 

Wouldn't this be simply a combination of 12 items taken 2 at a time .... maybe you call it 12 choose 2. 

 

                                                  12C2  =  66  

 

I looked it up online what 12C2 is because I'm lazy.  The actual way to calculate 12C2 is:  

 

                                                          12!  

                                                   —–————   =  66  

                                                   2! • (12 – 2)!  

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