An urn contains 6 green balls and an unknown number, which is ≤ 6, of blue balls. Three balls are drawn successively at random, and not replaced and are all found to be blue.

Determine the probability that a green ball will be drawn at the next draw.

There is an equal chance that there are 3, 2, 1, or 0 Blue Balls [BB] left in the urn. [Probability = 0.25]<o:p></o:p>

In each of the cases the probability of getting a green ball would be:<o:p></o:p>

3 BB = 6/9<o:p></o:p>

2 BB = 6/8<o:p></o:p>

1 BB = 6/7<o:p></o:p>

0 BB = 6/6<o:p></o:p>

Adding up gives a probability of 0.81<o:p></o:p>

Posted by Syzygy on 2010-05-19 12:49:45