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!
Friday, July 13, 2012
I have four wings, but cannot fly, I never laugh and never cry; On the same spot I'm always found, toiling away with little sound.