A friendly game of cards

If you're short of money and don't want to work, beg, borrow, or steal for it, here's a dandy way to make some significant moolah: Ask your best friend, we'll call him Joe, over for a game of cards. As an incentive, tell Joe you'll get in a case of his favourite brew. After he's got a brew or two inside, start playing the following game. 

From a deck of cards, select an ace and four kings and place them randomly face down on the table. Ask Joe to select a card but leave it face down. Tell him that as part of the game you are permitted to peak at the remaining cards and will turn three of them over. You do so and they are all kings. There are now two cards face down on the table: obviously, they have to be an ace and a king.

Tell Joe that with two cards on the table, one of which has to be an ace and the other a king, the odds are even  that the card he has selected is the ace. However, to make the game attractive, say you will give him 3:2 odds each time he bets $20. That is, Joe will win thirty dollars half the time he plays. A simple calculation shows that if he plays a hundred games he stands to win $500. Joe, feeling that with such odds he can’t lose, plays the game over and over far into the night.

‘Boy, you are sure one lucky SOB,’ Joe says as he departs for home many hundreds of dollars poorer. Joe vows to come back and play the game another night when his luck will surely be better.

Of course, you've already figured out that Joe was a sucker to play the game under the stated conditions. You decide that before Joe figures out how he was hosed, you'll invite your other pals over to suffer the same fate.