On a table there are two bags. The first contains one white marble. The second bag contains one red and one white marble. Blindfolded, Billy takes one marble out of the second bag and puts it in the first bag. He then takes off his blindfold and takes a marble out of bag one. It is a white marble.
What is the probability that the other marble in the first bag is also a white marble?

Dutch National Science Quiz 12/24/2004

before i look at the solution i wonder why this isn't a 50/50 chance?

since the blind pull was between one marble of each color after the blind pull there was a 50/50 chance of both marbles in the first bag being white.

edit: okay the probability is for a single marble and not both being white.

Edited on October 15, 2005, 12:26 am

Posted by tanx on 2005-10-15 00:21:26