12.     Suppose we have four boxes A,B,C and D containing coloured marbles as given below:


One of the boxes has been 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 box A ?

Answers (1)
S seema garhwal


Let R be the event of drawing red marble.

Let E_A,E_B,E_C  respectively denote the event of selecting box A, B, C.

Total marbles = 40

Red marbles =15


Probability of drawing red marble from box A  is P(E_A|R)

                          P(E_A|R)=\frac{P(E_A\cap R)}{P(R)}