9656 /www/nrich/html/content/id/9656/ 10 2012-11-15T11:20:54 <?xml version="1.0" encoding="UTF-8"?> <mdoxml version="1.0">These problems challenge you to find all possible solutions. One of the best answers to "How do you know you have found them all" is to be able to say "I worked systematically!"</mdoxml> 2 3 0 0 0 0 0 Header for 9655