I first saw these on the blog of Steve Natasiuk. [url]http://mathonthemckenzie.blogspot.com/search?q=macmahon[/url][br][br]The first question: given squares divided in four parts and three colors, how many are possible? (This sketch is a spoiler, but it's still a fun puzzle. Sort them to be sure you have them all.)[br][br]Then you can start to think like Percy MacMahon: what mathematical questions can you ask?[br][br]One classic is: can you make a rectangle where all the edges match color? [br]Percy liked to ask can you make one with all the same color on the outside edge?[br][br]Can you make 2 different rectangles at the same time using all the tiles with each rectangle with a constant color edge? Three rectangles?[br][br]A bit more about these at [url]http://bit.ly/primesquares[/url]