http://www.mathscore.com/math/practice/Percentages/
http://www.mathscore.com/math/practice/Compound%20Interest/
http://hotmath.com/help/gt/genericalg2/section_9_4.html
http://www.ucl.ac.uk/Mathematics/geomath/level2/mat/mat3.html
http://www.intmath.com/matrices-determinants/4-multiplying-matrices.php
http://www.mathwarehouse.com/algebra/matrix/inverse-of-a-matrix.php#answer
http://hotmath.com/help/gt/genericalg2/section_4_4.html
http://algebralab.org/lessons/lesson.aspx?file=Algebra_matrix_systems.xml
http://www.kutasoftware.com/FreeWorksheets/Alg2Worksheets/Systems%20of%20Two%20Equations%20Cramers%20Rule.pdf
http://amby.com/educate/math/4-2_pr_x.html
http://www.regentsprep.org/Regents/math/algtrig/ATS5/PCPrac.htm
http://hotmath.com/help/gt/genericalg2/section_9_4.html
http://www.regentsprep.org/Regents/math/ALGEBRA/APR2/PracPerm.htm
http://questions.ascenteducation.com/iim_cat_mba_free_sample_questions_math_quant/permutation_combination/
http://www.mathgoodies.com/lessons/vol6/intro_probability.html
http://www.thatquiz.org/tq-d/
http://www.mathgoodies.com/lessons/vol6/challenge_vol6.html
http://www.regentsprep.org/Regents/math/ALGEBRA/APR3/PracCond.htm