Perl script reveals math trick


Article from Issue 87/2008

A trick that anybody can learn lets you determine the day of the week from the date. We’ll apply some Perl technology to discover whether the method is reliable.

Recently, I was reading Mind Performance Hacks and stumbled across Hack Number 43, which explains how to determine the day of the week for any given date. The method is attributed to Lewis Carroll], the author of Alice’s Adventures in Wonderland. Simply calculate four values, one after the other, for the year, month, and day, and a fourth value as an adjustment factor. Then add the values, divide by 7, and the remainder amazingly gives you the day of the week as a number between zero (Sunday) and six (Saturday).

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