Critical Thinking Puzzles

This link contains enough tough puzzles to test your mental powers for hours and hours. When we think critically we become better learners. We don't just accept facts, we explore them, uncovering connections and identifying the often hidden cause-and-effect relationships. Try this intriguing array of puzzles, challenges, funky facts, things to build, weird riddles, and other brain teasers. Some are old favorites that never fail to stump, others are totally new, but all promise hours of fun.
http://mathforum.org/k12/k12puzzles/critical.thinking/puzz5.html