There are two I and II. The bag I contains 3 white and 4 black balls, and bag II contains 5 white and 6 black balls. One ball is drawn at random from one of the bags and is found to be white. Find the probability that it was drawn from the bag I.

Let W : White ball


B : Black ball


X : 1st bag


Y : 2nd bag


Assuming, selecting bags is of equal probability i.e.


We want to find P(X|W), i.e. probability of selected white ball is from the 1st bag






Conclusion: Therefore, the probability of selected white ball is from the 1st bag is


1