You want to send a valuable object to a friend. You have a box which is more than large enough to contain the object. You have several locks with keys. The box has a locking ring which is more than large enough to have a lock attached. But your friend does not have the key to any lock that you have. How do you do it? Note that you cannot send a key in an unlocked box, since it might be copied.
Locked and safe
5 random riddles
Walking home one day, you take a short cut along the train tracks. The tracks cross a narrow bridge over a deep gorge. At the point you are 3/8 of the way across the bridge, you hear the train whistle somewhere behind you. You charge across the bridge, and jump off the track as the train is about to run you down. As it happens, if you had gone the other way, you would have reached safety just before being run over as well. If you can run ten miles per hour, how fast is the train moving?
A man buys a rope from a woman for $3.00 and hands the woman a $10 bill. The woman goes into the grocery store next door to get change. She returns and gives the man $7.00. After the man leaves, the clerk from the store comes and says, "Hey, that was a counterfeit bill you gave me." The woman gives the clerk a good bill.
How much has the woman lost?