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Simple coins (Posted on 2002-04-09) Difficulty: 2 of 5
I toss two coins and look at the outcome. I then tell you that at least one of the coins is showing up as "tails". What is the chance that the other one is showing "tails" as well?

(from techInterview.org)

See The Solution Submitted by art    
Rating: 3.8750 (16 votes)

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re(5): Solution Using Real Prob/Stats | Comment 31 of 45 |
(In reply to re(4): Solution Using Real Prob/Stats by Charlie)

Charlie, you have a valid point here (and Lee, I think, has encapsulated it very well a couple of comments back).

(And I have read the full set of comments), but the issue that you are talking about is definitely not the issue that Eberhard and I were talking about. (Which translates to Lee's case (i) and maybe (ii)).

As evidence of what Eberhard was discussing, I will quote his earlier postings:
...the real answer and why are as follows: The first know that each toss is concidered a seperate event by probability (known as independence)- meaning that the probability of either coin showing a particular side is always one half 1/2. Second know that when trying to determine if both will be the same side the probabilities are multiplied, i.e. 1/4 (this can be thought of as an ordered sequence).
-- and --
...what i think you might be missing is that HT and TH are functionally equivilant, meaning that there are 2 not 3 outcomes even in art's solution...
Edited on December 4, 2003, 7:44 am
  Posted by SilverKnight on 2003-12-04 07:23:49

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