Mixing Up Music: When is a random shuffle random?

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Last Saturday (April 5), a listener contacted Weekend Edition on National Public Radio wondering why, when her Ipod was on random mode, the same songs kept coming up. Math Guy Keith Devlin (of the monthly math column Devlin’s Angle) answered her question by explaining that randomness is different from uniform distribution: unless your Ipod is set to simply shuffle the songs or to play certain favorites more than others (which are both options), the random mode really is random: when a song finishes, it’s just as likely as any other song to be picked to played next. Indeed, if you play enough songs (where enough depends on just how many songs you’ve got on there) you’d absolutely expect there to be times when the same song is played not just frequently, but several times in a row.

You can listen to the 4½ minute NPR snippet over here.

Thanks to Daniel Birmajer for bringing this to our attention!

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