Imagine you have committed a crime. As punishment you need to enter one of three rooms. Room 1 is full of blazing fire, Room 2 is filled with terrorists waiting to kill you, Room 3 is filled with hungry tigers who haven't eaten in months. Which should you choose?
When David was eight years old, he hammered a nail in a tree to mark his height. Seven years later at age fifteen he returned to see how mush higher the nail would be. If the tree grew at nine centimetres each year since he was eight, how high would the marking be?