Question

Bag I contains 3 red and 4 black balls and Bag II contains 4 red and 5 black balls.One ball is transferred from Bag I to Bag II and then two balls are drawn atrandom (without replacement) from Bag II. The balls so drawn are found to beboth red in colour. Find the probability that the transferred ball is red.

Answer 1

let the event of drawing a red ball frm bag 2 be p(A)
p(A)=4/10,
let event of drawing second red ball frm bag 2 is p(B/A)
p(B/A)=3/9
so,the probability of drawing two red balls frm bag 2 is
p(AпB)=4/10.3/9=12/90

(this is the case if the ball transfered frm bag 1 to bag 2 is not red..)