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 Red ball... Red ball (Posted on 2002-10-17)
If you take two balls randomly out of a jar of colored balls, there is a 50% chance that the balls will both be red.

What is the total percentage of red balls in the jar?

 Submitted by levik Rating: 3.1538 (13 votes) Solution: (Hide) This turns out to be a more difficult (and somewhat deceptive) problem than I first thought. The answer is that 75% of the balls are red. This is because the only viable solution seems to be when there are a total of 4 balls, and 3 of them are red. (You cannot get the same results with 8 balls 6 of which are red, etc) TomM has submitted a fairly rigorous proof to this in the problem's comments.

Comments: ( You must be logged in to post comments.)
 Subject Author Date re: Another solution (re: a mathematecally more rigorous solution) Ady TZIDON 2015-08-22 03:34:06 Not everything appears as it seems Dej Mar 2011-09-13 03:24:48 I do not agree with the official solution ajosin 2005-03-04 19:53:25 Comment on official solution Nick Hobson 2004-09-18 18:20:52 re: solution - and my own one sassy 2004-05-13 19:36:19 easy Billy Bob 2004-03-28 10:22:38 Red ball... Red ball Paula Bilton 2003-08-14 08:16:42 (easy) Solution Chaz 2003-05-03 14:41:37 Another solution (re: a mathematecally more rigorous solution) Charlie 2003-02-17 14:36:06 solution Keedom 2002-11-18 23:43:54 Answer Dulanjana 2002-10-18 17:11:03 is this right? hai 2002-10-18 17:02:51 a mathematecally more rigorous solution TomM 2002-10-18 02:46:53 typo TomM 2002-10-18 00:07:54 Exactly! TomM 2002-10-18 00:01:45

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