Question: If you have an 11 minute and 13 minute hourglass, how can you accurately time 15 minutes?
Answer: Start both hourglasses then when the 11 minute hourglass has finished immediately flip it again. When the 13 minute hourglass runs out the 11 minute hourglass will have 9 minutes left, so flip it and it will last another 2 minutes, 13 minutes + 2 minutes = 15 minutes.
Question: A wise person was once sentenced to death by a king. The king couldn't decide how to execute him so he said to the wise person, you can say anything you want, if it is true, I will hang you, if it is not true I will shoot you. In the end the king released the wise man. What did the wise man say?
Answer: You will definitely shoot me.