Wednesday, July 29, 2009

What're the Odds?


I'm not even sure that I know how to ask the right question: that's why I need some help from a mathematician/logician/probabilityician.

On Radio 3 this morning, at about 0715, the chap on the Breakfast programme played the Gloria from William Byrd's mighty Mass for Five Voices. It's a rather quiet piece, and not terribly audible on the M40 at 70mph, so I switched over to my iPod, which was on shuffle. And swipe me if the next iPod track that came on after the currently-playing Prokofiev's The Wedding of Kije wasn't the Gloria from William Byrd's Mass for Five Voices.

Now, the question I'm trying to frame more precisely is "what're the odds of that happening?" (i.e. the same track on the radio being followed by that very track on my iPod).

I guess the elements I'd expect to be in the equation are:
  1. The number of tracks on my iPod (9,738)

  2. Some way of carving up the time that Radio 3's been broadcasting (e.g. into 5-minute slots)

  3. The number of tracks in Radio 3's record library (let's call that nt)

And thus there'd be some kind of sum that outputted a probability value.

But I have no idea how to start doing this sum. Can anyone help? Thanks.