Card Flip Magic
Instructions
This activity requires a Magician (who knows how to do it) and a Player.
1. Somebody click "Twiddle Tiles" to generate a random 5x5 field of squares.
2. Magician clicks on remaining 11 squares to set their colors. Now the field is 6x6.
3. Magician looks away. Player clicks any one square to change its color.
4. Magician looks at field and finds the square that Player flipped.
This is (somewhat ironically) a digital version of Activity 4: Card Flip Magic from the CS Unplugged. Go there for full instructions.
I made this applet because I don't have magnets to make a presentation set. If you're working on a flat surface (hello, document camera!), any two-sided object (playing cards, two-color-tiles, etc.) can do the same job.