Compilation of Probability based problems
http://gmatclub.com/forum/math-probability-87244.html
http://franky4gmat.blogspot.com/2004/09/quantitative-probability.html
http://www.benbest.com/science/theodds.html
http://gmat.jumbotests.com/tests/get/score/47e28cab3b74257e1ef06e8a9fc69c42ed338118/98910?utm_campaign=gmat&utm_content=gmat-probability-questions&utm_medium=email&utm_nooverride=1&utm_source=test-results