Probability

http://www.greencastle.k12.pa.us/high%20school/math/probabil/page10.html

http://www.mathwarehouse.com/probability/combination.php

http://regentsprep.org/Regents/Math/combin/excomb.htm

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

http://questions.ascenteducation.com/iim_cat_mba_free_sample_questions_math_quant/permutation_combination/

http://www.wtamu.edu/academic/anns/mps/math/mathlab/col_algebra/col_alg_tut57_comb.htm

http://www.tpub.com/math2/78.htm