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September 24th, 2009, 10:05 PM  #1  
Newbie Joined: Sep 2009 Posts: 8 Thanks: 0  Simple probability problem...
...for some, but not for me. Quote:
Thanks and cheers, Tyster  
September 24th, 2009, 10:24 PM  #2 
Senior Member Joined: Oct 2007 From: Chicago Posts: 1,701 Thanks: 3  Re: Simple probability problem...
You know the probability of each one landing heads is 1/2. (And tails is 1/2) And when we want "x to happen" AND "y to happen" AND ..., we have to multiply the probabilities. And finally, when we want "x to happen" OR "y to happen" OR..., we have to add the probabilites. For exactly 2 heads, we need 3 tails. So, what is the probability of 2 heads, and 3 tails? But we need *at least( 2 heads: So, we can add: P(exactly 2 heads) + P(exactly 3 heads) + P(exactly 4 heads) + P(exactly 5 heads). Or, we can realize that P(X happens) = 1P(X doesn't happen), and we can add: P(0 heads) + P(1 head), and subtract that from 1. There's a slightly more advanced way of doing this (using combinations), but this is a simple enough problem that it's more trouble than it's worth. 
September 27th, 2009, 04:48 PM  #3 
Newbie Joined: Sep 2009 Posts: 8 Thanks: 0  Re: Simple probability problem...
Thanks for the explanation. Cheers.


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