JEE Main 2021 · MathsMultiple choiceSingle correctMediumMulti-step

JEE Main 4 August 2021, Shift 1, Maths Q78

Question 78 of 90 in this shift, Maths question 18 of 30, Section A.

Two players A and B play a game. Player A first throws a fair die and if 5 or 6 appears, he wins; otherwise player B throws a fair coin and wins if head comes. The process continues till someone wins. The probability that B wins after completion of 3 or more throws of the die, is

(1) $\frac{1}{18}$ Official answer
(2) $\frac{1}{9}$
(3) $\frac{4}{9}$
(4) $\frac{1}{2}$

Official answer

Option 1

NTA final key.

Chapter: Probability
Topic: Conditional Probability
Idea tested: Conditional Probability in Infinite Games

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Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.