Binary Trick

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Grade Vs Difficulty:
  EasyModerateChallengingPerplexing
1-2
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5-6
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13-14

In this trick, someone is asked to pick an integer from 1 to 31 and identify which of five cards contains the number. The person running the trick can then name the number.
This trick may be used with other lessons that require binary numbers such as the game of Nim.

It can be viewed in this context at:
Game of Nim

Slides describing the trick in more detail are available
here.