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Four balls (Posted on 2017-05-19) Difficulty: 2 of 5
There are four balls in a hat: a blue one, a white one, and two red ones. Now I draw simultaneously two balls, look at them, and announce that at least one of them is red.

What is the chance that the other is red as well?

See The Solution Submitted by Ady TZIDON    
Rating: 3.5000 (2 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
re(5): Who's right | Comment 15 of 22 |
(In reply to re(4): Who's right by Charlie)

External agent?  Ady, or whoever is looking at the balls, is telling us something about the pair he draws.  We are asked to make a probability calculation from his statement.

You write "randomly chosen one of the balls".  You cannot assume just one ball is the basis of the decision when the problem uses "look at them", which means that Ady looks at both balls to make his statement.
  Posted by Brian Smith on 2017-05-21 23:17:59
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