Cut the knot: learn to enjoy mathematics
A math books store at a unique math study site. Learn to enjoy mathematics.
Terms of use
Privacy Policy

More Mathematics
CTK Exchange

Games to Relax
Guest book
Recommend this site

Sites for teachers
Sites for parents

Manifesto: what CTK is about Buying a book is a commitment to learning Things you can find on CTK Email to Cut The Knot Recommend this page

Barcode Magic

The ubiquitous barcodes serve as the basis for the following computer magic. The applet below is made to represent the standard barcode representation of the UPC-A codes. This is something that is commonly (and not quite correctly) referred to as the barcode. Do the following: pick up a product. It could be a bottle of Cola, an ice cream pack, or anything else with an UPC-A code and a barcode on it. Initially the applet displays 12 question marks. By clicking on them you can upgrade each to any decimal digit. Do this with 11 digits and leave one question mark. Press the "Check" button. The computer will announce the missing digit.

If this is not magic, what is?

<hr> <h3> This applet requires Sun's Java VM 2 which your browser may perceive as a popup. Which it is not. If you want to see the applet work, visit Sun's website at, download and install Java VM and enjoy the applet. </h3> <hr>

Copyright © 1996-2008 Alexander Bogomolny