Here's the question, from Russell Roberts' The Invisible Heart: An Economic Romance
'I know,' Sam said. 'First day of class, senior year of high school, and already a quiz. Don't worry. It's easy.'
He went to the board and wrote down two numbers: 531,000,000,000 and 16,500,000,000.
'The first number, 531 billion, is the amount of crude oil, measured in barrels, that's still under the ground. They're called reserves. The second number is the world's annual consumption of crude oil. Here's the quiz: when will the world run out of oil? You have one minute.' "
You can either read the rest of the chapter for the answer, or read Phil Miller
. My suggestion would be to read both, over and over, until you get it.