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Question: Answered & Verified by Expert
A fair die is thrown until 2 appears. Then the probability, that 2 appears in even number of throws, is
MathematicsProbabilityJEE MainJEE Main 2024 (29 Jan Shift 1)
Options:
  • A 56
  • B 16
  • C 511
  • D 611
Solution:
2717 Upvotes Verified Answer
The correct answer is: 511

Let the probability of 2 appearing in a throw be given by P2 and the probability of 2 not appearing be given by P2'.

P2=16, P2'=56

Now, we want 2 to appear in 2nd throw or 4th throw or 6th throw ... and so on

So, required probability is given by,

PE=56×16+563×16+565×16+...

PE=16×561-2536

PE=16×561136

PE=56×3611×16

PE=511

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