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?

(In reply to no expert by nellie)

In reply to Nellie, who wrote "I don't understand probablity. Since the first ball picked is then replaced, does it have any relevance what colour it was?"

The relevance of the color of the first ball, is that it indicates that it was probably drawn from the bag where marbles of that color predominate.

Posted by Dan on 2003-10-14 19:40:29