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Painfully Easy: Solution not correct

The second coins' chance of being heads is 50% - since it cannot know and is not affected by the first coins' result.
33% is complicating matters - hence the name.

Sarah M
Saturday, October 9, 2004

As far as I see, 33% is correct. This is because we are not told, *which* coin shows head.

As stated in the given answer, there are 4 possibilities:


For we know that at least one of the coins shows a head,

HH, HT and TH

remain. And only one of the three is the one we are looking for.

The situation is completly different, if we are told that the *first* coin shows head. In this case, only 2 possibilities remain:


Hence, the possibility is 50%.

It is correct that both coins are independend and the possibility for each of them to show head is one half. But: In the given problem we are not regarding one, but two. This is the difference.

Gerd Riesselmann
Monday, October 11, 2004

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