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Why repeating a digit may improve security on your iPhone’s 4-digit lockscreen PIN – Mind Your Decisions

Posted on January 10th, 2012 at 1:38 by Desiato in category: News, Puzzle


Am I helping myself by using three numbers in a four-digit code?

There are 4! = 24 possible ways a password can be formed from four distinct and known numbers. Will using just three numbers increase the number of possibilities?

The surprising answer is that yes, it does.

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Burning Time

Posted on January 27th, 2010 at 9:05 by John Sinteur in category: Puzzle


You have two one-hour fuses: If you light one, it will be consumed in exactly one hour.Unfortunately, they’re badly made — some sections of each fuse burn faster than others. You know only that each full fuse will burn in one hour.Using only these two fuses and matches to light them, how can you tell when 45 minutes have passed?

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  1. light both ends of first fuse, and one end of 2nd fuse at the same time. 30 min later, first fuse (lit both ends) will burn out. At this point, light the 2nd end of 2nd fuse (still burning from one end). 15 min later, 2nd fuse will burn out. Total = 45 min.

  2. Ooh. yj, that’s clever. (:

    Hey, John, maybe you should come up with another category for puzzles? They’re not news. ;p I like them!

  3. Yeah… when I can’t think of a category, I just leave it defaulting to “news”. Perhaps I should rename it to “bog if I know how to call this” or something…

  4. This was a puzzler on the NPR radio show “Car Talk” a year or 2 ago. Still, it’s neat.