# Mathematical Digest

### Short Summaries of Articles about Mathematics

in the Popular Press

"It's a kind of magic," by Ian Stewart. *New Scientist,* 4 January 2003, pages 38-39.

A magician asks someone to choose 5 cards from a randomly shuffled deck. Thecards are handed to the magician's assistant, who reveals 4 of the cards. Themagician, to great applause, says what the hidden 5th card is. In thisarticle, Stewart explains how this card trick works and why it has connectionsto information theory. The underlying idea is that one can communicate amessage using a very small amount of information, provided the information isarranged and communicated in just the right way.

*--- Allyn Jackson*