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 #1
avatar+33663 
+5
Apr 4, 2015
 #11
avatar+118723 
+6

Okay I am just starting to get somewhere.

I am looking at how many ways even numbers of people can be paired off

This post is NOT directly related to the question above.

 

4 people   ABC and D

AB CD

AC BD

AD BC

that is 4 people can be paired off in 3 ways

Now, before I wanted to do it as 4C2 which is 6

This would give the 6 above but each time you get one pair you automatically get the another pair so it can be seen that this will be too big by a factor of 2   so it is   4C2/2 = 6/2=3

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6 People

Now I am going to look at 6 people  A B C D E and  F

AB    there  are four more so they can be paired up 3 ways

AC    3 ways

AD    3 ways

AE     3 ways

AF     3 ways

Total = 3*5 =15

So 6 people can be paired off  15 ways.   This is  (6-1)(4C2)/2  = 15

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8 People

Now I am going to look at 8 people  A B C D E F G and H

AB   then 6 more =  15 ways

AC   then 6 more =  15 ways

AD   then 6 more =  15 ways

AE   then 6 more =  15 ways

AF   then 6 more =  15 ways

AG   then 6 more =  15 ways

AH  then 6 more =  15 ways

That is a total of  7*15=105    (8-1)(6-1)4C2/2 = 7*5*3

that is 8 people can be paired off in 105 ways

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So   2K people can be paired off in   3*5*7*......*(2K-1)   ways

 

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So   4 people are paired (and the pairs are then considered as 1)

they are then put clockwise into a cirlce (or anticlockwise)  rotations are considered the same.

The number of ways this could be done is  4*1=4 ways

6 people - it could  be done   5*3*2! = 30 ways

8 people - it could be done  7*5*3*3! = 1050 ways

2K people - it could be done  (2k-1)(2k-3)....5*3*(k-1)!

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Apr 4, 2015

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