AustMS Gazette Puzzle Corner 26

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

"Counterfeit coins

There are 20 coins in front of you, two of which are counterfeits. The genuine coins
are identical in weight, but the counterfeits are slightly lighter. Can you identify
10 genuine coins by using a balance-scale twice? Note that the two counterfeits
are not necessarily the same weight as each other." 

You can find the Puzzle Corner, as well as the entire Gazette online at:
http://www.austms.org.au/Gazette+Volume+39+Number+1+March+2012

Check it out when you feel like trying out random fun problems, and be sure to
send your solutions in.  A $50 book voucher is up for grabs for the best submission.  

Please e-mail solutions to ivanguo1986@gmail.com or send paper entries to: Kevin White,
School of Mathematics and Statistics, University of South Australia, Mawson Lakes SA
5095 

The deadline for submission is 1 May 2012.  The solutions will appear in the July
2012 issue of the Gazette.  

Thank you

Ivan Guo