Four cards are laid out before you, each with a letter on one side and a number on the other. You see E, 2, 5 and F. Which cards should you turn over that will prove the following rule: If there is an E on one side, the number on the other side must be a 5? See the answer by Manil Suri, Professor at University of Maryland, in this April 15 New York Times article that asks “Does Math Make You Smarter?”.
As to whether math really does make you smarter, the answer remains unclear. However, those who do well with numbers make far more money. That is not surprising, but the multiplier may be. See this U.S. News report (or not if you failed the test above) for the statistics.