JEE PYQ: Probability Question 29
Question 29 - 2020 (09 Jan Shift 1)
In a box, there are 20 cards, out of which 10 are labelled as A and the remaining 10 are labelled as B. Cards are drawn at random, one after the other and with replacement, till a second A-card is obtained. The probability that the second A-card appears before the third B-card is:
(1) $\frac{9}{16}$
(2) $\frac{11}{16}$
(3) $\frac{13}{16}$
(4) $\frac{15}{16}$
Show Answer
Answer: (2)
Solution
$P(AA) + P(ABA) + P(ABBA) + P(BAA) + P(BABA) = \frac{1}{4} + \frac{1}{8} + \frac{1}{16} + \frac{1}{8} + \frac{1}{16} + \frac{1}{16} = \frac{11}{16}$.
BETA
