Medium MCQ +4 / -1 PYQ · JEE Mains 2023

Let $\mathrm{S} = \{ {w_1},{w_2},......\}$ be the sample space associated to a random experiment. Let $P({w_n}) = {{P({w_{n - 1}})} \over 2},n \ge 2$. Let $A = \{ 2k + 3l:k,l \in N\}$ and $B = \{ {w_n}:n \in A\}$. Then P(B) is equal to :

  1. A $\frac{3}{32}$
  2. B $\frac{1}{32}$
  3. C $\frac{1}{16}$
  4. D $\frac{3}{64}$ Correct answer

Solution

<p>$P({w_1}) + {{P({w_1})} \over 2} + {{P({w_1})} \over {{2^2}}}\, + \,..... = 1$</p> <p>$\therefore$ $P({w_1}) = {1 \over 2}$</p> <p>Hence, $P({w_n}) = {1 \over {{2^n}}}$</p> <p>Every number except 1, 2, 3, 4, 6 is representable in the form</p> <p>$2k + 3l$ where $k,l \in N$.</p> <p>$\therefore$ $P(B) = 1 - P({w_1}) - P({w_2}) - P({w_3}) - P({w_4}) - P({w_6})$</p> <p>$= {3 \over {64}}$</p>

About this question

Subject: Mathematics · Chapter: Probability · Topic: Classical and Axiomatic Probability

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