Bags of Marbles Puzzle
You have three bags, each containing two marbles. Bag A contains two white marbles, Bag B contains two black marbles, and Bag C contains one white marble and one black marble.
You pick a random bag and take out one marble.
It is a white marble.
What is the probability that the remaining marble from the same bag is also white?
@Ramani Aswath Good try sir but answer is 2/3.
2/3 (not 1/2)
You know that you do not have Bag B (two black marbles) so there are three possibilities
You chose Bag A, first white marble. The other marble will be white
You chose Bag A, second white marble. The other marble will be white
You chose Bag C, the white marble. The other marble will be black
So 2 out of 3 possibilities are white.
Why not 1/2? You are selecting marbles, not bags.
You already have a bag and have already chosen a marble, which is white. The bag has to be white-white or white-black. So the only choices left are white if it is a white-white bag or black if it is a white-black bag.
So it is 50-50.