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Red ball... Red ball (Posted on 2002-10-17) Difficulty: 4 of 5
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?

See The Solution Submitted by levik    
Rating: 3.1538 (13 votes)

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I do not agree with the official solution | Comment 13 of 15 |
The real answer is that the total percentage of red balls in the jar varies discretly from 3/4 (if the total number of balls is 4) to 1/sqrt(2) (if the total number of balls aproaches infinity).

Charlie gave a few possible values in his post.

This would have been a nice problem if the question had been "What is the smallest interval for the possible percentages of red balls?".

Answer; (1/sqrt(2), 3/4 ], or about 70.7 to 75.0 %.

And by the way, if the first ball is put back in the jar befor the second one is drawn, then there is a unique solution, and it is 1/sqrt(2).

Edited on March 4, 2005, 7:55 pm
  Posted by ajosin on 2005-03-04 19:53:25

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