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← IIT-JEE 2011 · Paper 1
MathematicsSingle correct+3 / -1Question 62 of 69

IIT-JEE 2011 · Paper 1, Mathematics question 62

Passage

Paragraph for Question Nos. 61 and 62

Let U1U_1 and U2U_2 be two urns such that U1U_1 contains 3 white and 2 red balls, and U2U_2 contains only 1 white ball. A fair coin is tossed. If head appears then 1 ball is drawn at random from U1U_1 and put into U2U_2. However, if tail appears then 2 balls are drawn at random from U1U_1 and put into U2U_2. Now 1 ball is drawn at random from U2U_2.

Given that the drawn ball from U2U_2 is white, the probability that head appeared on the coin is

Choose one option
Answer and worked solution

Official answer: D

Bayes.
P(H∣W)=12⋅452330=1223.P(H\mid W)=\frac{\frac12\cdot\frac45}{\frac{23}{30}}=\frac{12}{23}.

(D)