AustMS Gazette Puzzle Corner 32

The Australian Mathematical Society Gazette’s Puzzle Corner is a regular column with
entertaining mathematical puzzles, here’s an example: 

"Colour coordination 

I need to hang 20 garments on a clothes line.  Each garment requires two pegs.  I have
20 green and 20 red pegs.  I choose pegs at random.  On average, how many garments will
have pegs of the same colour?" 

You can find the Puzzle Corner 32 online at:
http://www.austms.org.au/Publ/Gazette/2013/May13/Puzzle.pdf 

Check it out when you feel like trying out some fun problems, and be sure to email your
solutions to ivanguo1986@gmail.com.  A $50 book voucher is up for grabs for the best
submission.  The deadline for submissions is 1 July 2013.  The solutions will appear in
the September 2013 issue of the Gazette.  

Thank you 

Ivan Guo