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Dishonest Strategy (Posted on 2005-07-16) Difficulty: 3 of 5
I have the perfect strategy to win any sort of game of chance. Just when I lose, I say , "2 out of 3?" and my opponent always accepts due to my infinite persuasiveness. If I lose again, I propose 3 out of 5, then 4 out of 7, etc.

Essentially, the effect of this strategy is that if the number of games I have won ever exceeds the number of games won by my opponent, then I win overall.

If I have a 50% chance to win any one game, what is the probability that I will eventually win overall (or rather, what does the probability approach)?

What if we play a game that involves a little strategy, and I only win 1/3 of the games?

See The Solution Submitted by Tristan    
Rating: 4.0000 (2 votes)

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Solution Solution (not 100%) | Comment 5 of 18 |


You will win at least 50% of the games on the first try

If you lose the first toss/roll/etc., then you go to "2 out of 3", at which point you must win twice to win overall.  You only have a 25% chance of doing that which means you will win 1/8 (overall) of the games on 3 tosses/rolls/etc. (in addition to the 50% won on the first roll)

So the sum is not 1/2 + 1/4 + 1/8 ...  It's 1/2 + 1/8 + 1/32 which converges to 2/3.  The remaining games will continue on as you infinitely expand your opportunities to win.

Likewise, with a 1/3 chance of winning, the series converges to 3/8.

Edited on July 18, 2005, 9:35 pm
  Posted by Bob Smith on 2005-07-18 13:58:17

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