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June 12th, 2017, 03:04 AM  #1 
Newbie Joined: Dec 2016 From: A place called UNIVERSE Posts: 8 Thanks: 0  Conditional probability
A double headed, a double tailed and an ordinary coin are placed in a tin can. One of the coins is randomly chosen without identifying it. the coin is tossed and falls "heads". Determine the probability that the coin is the double header.

June 12th, 2017, 11:34 AM  #2 
Senior Member Joined: Aug 2012 Posts: 1,626 Thanks: 413 
I say 2/3. Here is my reasoning. I'm sure there's a formal way to do this but I never learned basic probability theory so I just cranked out the possibilities. First, there are three coins labeled HH, TT, and TH. Note that these are just the names of the coins. Now if you pick HH, there are two possible flip outcomes: H or H (here H and T refer to outcomes). If you pick TT, there are two possible outcomes: T and T If you pick TH, there are two possible outcomes: T or H. Now we have six possible outcomes of a choice followed by a flip. Three are heads and three are tails. Out of the three heads outcomes, two of them came from the HH choice; and one from the TH choice. Therefore the odds are 2/3 that the original flip was from the doubleheaded coin. What say you, probability experts? Code: HH TT TH             H H T T T H ^ ^ ^ 1 2 3 Last edited by Maschke; June 12th, 2017 at 11:40 AM. 
June 12th, 2017, 12:32 PM  #3 
Newbie Joined: Dec 2016 From: A place called UNIVERSE Posts: 8 Thanks: 0 
Well thank u so much , u reached the right conclusion .... thanks for the help genius !

June 12th, 2017, 02:26 PM  #4  
Senior Member Joined: Aug 2012 Posts: 1,626 Thanks: 413  Quote:
 

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