A deaf and mute man goes to the train station. Tickets for the train are 50 cents each. The man goes to the ticket booth and hands the man inside just a dollar. The man in the booth hands him two tickets.
How did the man in the booth know to give him two tickets without even looking at him?
You have a 12 liters jug full of water. You have two empty 8 liters and 5 liters jug. How can you divide the water into two equal parts using these jugs?