If J can paint a room in 6 hours, and T can paint the same room in 12 hours, how long would it take J & T to paint the room together?
You have a square room whose walls are 4 mirrors. You are trying to hit a point in the room with a laser. Assuming the laser can go through the shooter, there are infinitely many ways to hit that point -- can you place a finite number of 'blocking' points such that you can't hit the original point?