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 Simpler probability problem? (Posted on 2015-08-11)
An urn contains 5 black and 20 white marbles. They are to be drawn one at a time until all of one color has been exhausted.

What is the probability that the color of the first draw correctly predicts the first color exhausted?

 No Solution Yet Submitted by Jer No Rating

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 re(3): solution | Comment 7 of 14 |
(In reply to re(2): solution by Charlie)

Let not be confused with the wordings:

.I SAID:..........IMHO  the probability you have evaluated  is the probability of matching (same color) of 1st drawn with the last of same color."  ;

it addresses the last i.e the exhausting one, -  we do not want to continue till the end.

All in all, continuing to read in this context I maintain that

the official solution re prediction is 2/3, not 1/3.

 Posted by Ady TZIDON on 2015-08-12 10:27:16

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