On Thu, Jun 18, 2015 at 6:13 PM, Ihe Onwuka <[email protected]> wrote:
> >> Pick a Box A. > > Sampling is without replaceent. > Chance of 1st ball being black = 3/6 = 1/2 > Chance of 2nd ball being black = 2/5. > > Chance of both being blank = 1//2 * 2/5 = 1/5. > > BUT there are 2 ways for Box A to have 2 black balls > > a). Box B could have zero black and Box C 1 black or > b) Box C could have zero black and Box B 1 white. > So multiply by 2 > > Se P (Box A has 2 black balls) = 1/5 * 2 = 2/5. > > BUT there is only a one in 3 chance of selecting Box A > > Final answer = 2/5 * 1/3 = 2/15 > > I settle for partial credit. > > Good thing I only aimed for partial credit as I got it wrong and I guess it is because I over-elaborated. If you've seen 1 black ball there are 5 other possible balls to choose from only 2 of which are black. No need to multiply the probability of picking that box (1/3) because that is given information. So by sampling without replacement the probability is 2/5. Final answer.
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