You choose one of two identical looking bags at random. One bag has three black marbles and one white marble. The other has three white marbles and one black marble.

After choosing a bag you draw one marble out at random. You notice it is black. You then put it back and draw another marble out of the same bag at random.

What is the probability that the second marble drawn is black?

the answer is fifty percent ... basically the first marble drawn being black is irrelevant in determining the probablity of the second one being black since we are replacing the marbles... this is exactly the same probability tree that ws suggested earlier except that 5/8 was the probability of drawing two black marbles but what we are asked is the probability that the second one would be black...

Posted by anand on 2003-10-17 14:38:05