I'm posting one puzzle, riddle, math, or statistical problem a day. Try to answer each one and post your answers in the comments section. I'll post the answer the next day. Even if you have the same answer as someone else, feel free to put up your answer, too!
Thursday, September 24, 2009
You Can See Through This One Right Away
It was invented in ages past to see through walls. It is still in use in some parts of the world today.