An Easy Card Trick for Fleecing Someone

Want to scam a little extra money?

By Alex Stone
Nov 28, 2006 6:00 AMNov 12, 2019 4:50 AM


Sign up for our email newsletter for the latest science news

Take three cards, one painted blue on both sides, one red on both sides, and a third red on one side and blue on the other. 

Have your mark blindly draw a card and display one side, keeping the other side hidden. Let's suppose the side you see is blue. 

Now explain that he clearly didn't draw the double-red card, so the card must either be blue on both sides or red and blue; then wager even money that the other side is blue. 

Sounds like a fair bet, right? Wrong. The probability is in fact only one-third that the other side is red. The visible side could be the blue side of the red-blue card, or it could be either of the two blue sides of the double-blue card. 

In two out of these three equally likely scenarios, the double-blue card is the one in his hand, so the probability is twice as great that the other side is blue. Don't forget to send me a cut of your winnings!

1 free article left
Want More? Get unlimited access for as low as $1.99/month

Already a subscriber?

Register or Log In

1 free articleSubscribe
Discover Magazine Logo
Want more?

Keep reading for as low as $1.99!


Already a subscriber?

Register or Log In

More From Discover
Recommendations From Our Store
Shop Now
Stay Curious
Our List

Sign up for our weekly science updates.

To The Magazine

Save up to 40% off the cover price when you subscribe to Discover magazine.

Copyright © 2024 Kalmbach Media Co.