smmore

http://www.800score.com/guidec7cview1a.html

http://www.mansw.nsw.edu.au/members/reflections/vol23no4yen.htm

http://www.questionbank.4gmat.com/mba_prep_sample_questions/permutation_combination_probability/

Start Here-
Overview of Combinations: http://regentsprep.org/regents/math/math-topic.cfm?TopicCode=combin
Overview of Permutations: http://regentsprep.org/regents/math/math-topic.cfm?TopicCode=permut

Advanced-
Everything you need to know about Permutations: http://www.urch.com/forums/gmat-math/24356-complete-guide-permutation-combination-probability-all-you-need-gmat.html
More Permutations: http://www.themathpage.com/aPreCalc/permutations-combinations.htm#perm%20
More Combinations: http://www.themathpage.com/aPreCalc/permutations-combinations-2.htm

Solve these problems-
http://www.urch.com/forums/gmat-problem-solving/25411-compilation-probability-problems-post148016.html