A Box contains black balls and white balls, with 1/2 of each. Now we add black balls, with 1/8 of total. What is probability of drawing 1 black, 2 black and 3 black balls respectively (no replication)? Analysis: Drawing one black ball : 1/8*1/2+1/2 = 9/16. Thinking of conditional probability, we simply consider what is left after first one drawn and multiply its probability to the first one. However, here, we only know probability of black ball(9/16). Please shed some light, what is probability of the second ball drawn is black, given first one is black ball? , and so on... Thanks for your attention.