Question

There are four boxes, A,B,C and D, containing marbles. A contains 1 red, 6 white and 3 black marbles; B contains 6 red, 2 white and 2 black marbles; C contains 8 red, 1 white and 1 black marbles; and D contains 6 white and 4 black marbles. One of the boxes is selected at random and a single marble is drawn from it. If the marble is red, what is the probability that it was drawn from the box A? Select the correct answer from above options

Answer 1

Let A : Ball drawn from bag A B : Ball is drawn from bag B C : Ball is drawn from bag C D : Ball is drawn from bag D BB : Black ball WB : White ball RB : Red ball Assuming all boxes have an equal probability for picking i.e. 1 4 We want to find P(A|RB), i.e. probability of selected red ball is from box A Conclusion: Therefore, the probability of selected red ball is from box A is 1 15