[math-fun] Balls in Bags

Let there be n balls in a bag. Let k_i be a partition of n such that there are k_1 red balls, k_2 blue balls, etc..., and k_a yellow balls. Give each ball an unique number from 1 to n. What is the probability that a red ball has a number <=j. e.g. consider a bag with 20 balls numbered 1..20, and randomly coloured red (7) and green (13). What is the probability that a red ball is numbered either 1 or 2? Jon Perry perry@globalnet.co.uk http://www.users.globalnet.co.uk/~perry/maths/ http://www.users.globalnet.co.uk/~perry/DIVMenu/ BrainBench MVP for HTML and JavaScript http://www.brainbench.com