Always Running

Three light switches are outside a closed door. Inside the room are three light bulbs, each controlled by one switch. You can only enter the room once. How can you determine which switch controls which bulb?

A king wants to send a message to his ally. The message must pass through several kingdoms, and each kingdom will keep a copy. How can he ensure the message is not altered?

A prisoner is told he will be hanged on a morning when he will not expect it. He reasons he cannot be hanged, but he is. How?

What becomes more valuable the more it is broken?

You have 12 identical-looking coins, but one is either slightly heavier or lighter than the others. You have a balance scale and can use it only three times. How do you identify the false coin?

Four people need to cross a bridge at night. They have one torch. The bridge can only hold two people at a time. Person A takes 1 minute to cross, B takes 2 minutes, C takes 5 minutes, and D takes 10 minutes. How can they all cross in 17 minutes?