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Coin tossing (Posted on 2004-06-11) Difficulty: 3 of 5
I threw a coin n times, and never got three tails in a row. I calculated the odds of this event, and found out they were just about even; 50%-50%. How many times did I throw the coin?

A second question: what were the chances of having not gotten three heads in a row either?

See The Solution Submitted by Federico Kereki    
Rating: 3.6667 (6 votes)

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Solution Solution? | Comment 1 of 25

It's been a while since I took probability and statistics...

The chance of getting 3 tails in a row is 1/8 (.5x.5x.5).  You would, on average, have to toss the coin 8 times to get that once, and you have a 7/8 chance of not getting it.

In order to increase your chance of getting 3 tails in a row to 50/50, you would have to use the additive principle, meaning that you would have to toss the coin 8 times (to get the 1/8 chance) 4 times in succession (to get 4/8) which means you would have to toss the coin 32 times.

  Posted by Erik O. on 2004-06-11 14:12:46
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