[math-fun] Russian Postal Problem

Another possibility I didn't see while skimming through solutions. The original statement said you could send a box with a combination lock. Send the ring in it, then after she phones you that she got the box, tell her the combination. The eavesdroppers get the news too late, and the post office would know there's no point waiting for somebody to send or call the information before the box arrives. -- Jim Gillogly