MIT | Ben Mezrich

This "Hi-Lo system" was used by the MIT blackjack team Ben Mezrich accompanied. They scored sets of cards based on their face value plus or minus a certain number of points. Like this:

Cards two through six were worth their face value plus one.

Cards 10 through Ace were worth their face value minus one.

Cards seven through nine had a neutral value of zero.

The teams kept a running count based on those values and adjusted the count based on how far the dealer was into his or her six decks, called a shoe in Vegas parlance. From there, quite a bit more math was involved, including factoring in each particular casino's edge over the players -- based on that casino's house rules. Bottom line for the card counters: It's pretty complicated.

What made it even harder, as is demonstrated in 21, is that the strategy required a team in order to work well, in part because operating as a team made it more difficult to get caught. Herein is the lesson for anyone who thinks he or she might like to give card counting a shot: Although card counting is not illegal, casinos can ban you for any reason, and most take the official position that card counters interfere with the gaming fun of other customers. So before you give it a try, keep in mind that the only thing you can count on is that counting cards will put a quick end to your Vegas fun. -- E.C.