For i = 1, 2, 3, Box i contains one Red ball and i Blue balls. A random ball is chosen from each Box, and the result is two Red balls and one Blue ball. For each i, calculate the probability that the blue ball came from Box i. Solution Chose 3 red balls from 6 red balls : 3C6 Chose 3 blue balls from 6 blue balls: 3C6 So Total ball that you chose is 6C12 So the probability is 3C6*3C6/6C12 =((6*5*4)/(1*2*3))*((6*5*4)/(1*2*3))/ ((12*11*10*9*8*7)/(1*2*3*4*5*6)) =0.4329004.