A Lotto bet is picking 6 numbers out of 49 -- if you pick the correct combination, you get the jackpot!

If N persons play, there will be many repeats, since it's highly probable that some combinations will be chosen by two persons or more. (This is known as the "birthday paradox".)

What's the expected number of DIFFERENT combinations that will be chosen, if N persons play? (Assume these persons pick their combinations totally randomly.)

(In reply to Stirling Perhaps by owl)

I've corrected the formula. It's 13,983,816*(1-(13,983,815/13,983,816)^N), rather than N*(1-(13,983,815/13,983,816)^N).  Somewhere in my mind I was thinking that N represented the 13,983,816, but that's of course not the case.

I've corrected it in my previous post as well.

Posted by Charlie on 2005-01-15 04:58:53