
Re: say I flip a coin 100 times...
Posted:
Apr 13, 2005 8:39 AM


In article <1113379258.158183.322260@g14g2000cwa.googlegroups.com>, "HERC777" <herc777@hotmail.com> writes: > On average, not the average. > > OKAY WELL DONE EVERYBODY.... (can you tell I taught the remedial > business principles class?) > > So the expected matching is 20 flips long then?
That's the expected longest initial matching. Approximately.
> you flip a bunch of coins. > a million peole flip a bunch of coins > > whats the expected match length?
If you're asking for the longest match length, irrespective of starting position and irrespective of which pair of people get the match, I get 50 coins, give or take.
You have 1,000,001 flippers. Which means that there are 1,000,001 * 1,000,000 / 2 possible pairings of sequences. And for each pairing of sequences there are 100 * 100 possible selections of starting position.
That's 20 + 20  1 + ~13 = 52 coins.
The true answer is likely a bit lower since a 52 coin match rules out about half the possible starting positions on each side of each pairing. So call it 50 coins.
> > shuddering to think how misinterpreted this will get..
Well, you need to clarify your assumptions up front.
John Briggs

