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JEE Main 202124 FebruaryMorning Shift
Exam
JEE Main
Year
2021
Date
24 February
Shift
Morning Shift
Subject
Mathematics
Chapter
Probability

JEE Main 2021 · 24 February · Morning Shift · Mathematics · Probability

Let B _ i (i = 1, 2, 3) be three independent events in a sample...

Let Bi(i=1,2,3){B}_{i}\left(i = 1, 2, 3\right) be three independent events in a sample space. The probability that only B1{B}_{1} occur is α,\alpha, only B2{B}_{2} occurs is βandonly\beta and only{B}_{3}occursisoccurs is\gamma .LetLetpbetheprobabilitythatnoneoftheeventsbe the probability that none of the events{B}_{i}occursandtheseoccurs and these4probabilitiessatisfytheequations(α−2β)p=αβprobabilities satisfy the equations \left(\alpha - 2\beta\right)p = \alpha\beta and \left(\beta - 3\gamma\right)p = 2\beta\gamma(All the probabilities are assumed to lie in the interval \left\left(0, 1\right)\right) Then P(B1)P(B3)\dfrac{P\left({B}_{1}\right)}{P\left({B}_{3}\right)} is equal to______.

Correct answer

0

Step-by-step solution

Let P(B1)=p1,P(B2)=p2,P(B3)=p3P\left({B}_{1}\right) = {p}_{1}, P\left({B}_{2}\right) = {p}_{2}, P\left({B}_{3}\right) = {p}_{3}

given that p1(1−p2)(1−p3)=α…(i){p}_{1}\left(1 - {p}_{2}\right)\left(1 - {p}_{3}\right) = \alpha \ldots \left(i\right)

p2(1−p1)(1−p3)=β…(ii){p}_{2}\left(1 - {p}_{1}\right)\left(1 - {p}_{3}\right) = \beta \ldots \left(ii\right)

p3(1−p1)(1−p2)=γ…(iii){p}_{3}\left(1 - {p}_{1}\right)\left(1 - {p}_{2}\right) = \gamma \ldots \left(iii\right)

and \left(1 - {p}_{1}\right)\left(1 - {p}_{2}\right)\left(1 - {p}_{3}\right) = p \ldots \left(iv\right)</p><p></p><p>⇒ \dfrac{{p}_{1}}{1 - {p}_{1}} = \dfrac{\alpha}{p}, \dfrac{{p}_{2}}{1 - {p}_{2}} = \dfrac{\beta}{p} and p31−p3=γp\dfrac{{p}_{3}}{1 - {p}_{3}} = \dfrac{\gamma}{p}

Also β=\alphapα+2p=3\gammapp−2γ\beta = \dfrac{\alphap}{\alpha + 2p} = \dfrac{3\gammap}{p - 2\gamma}

⇒\alphap−2αγ=3αγ+6pγ⇒ \alphap - 2\alpha\gamma = 3\alpha\gamma + 6p\gamma

⇒\alphap−6pγ=5αγ⇒ \alphap - 6p\gamma = 5\alpha\gamma

⇒p11−p1−6p31−p3=5p1p3(1−p1)(1−p3)⇒ \dfrac{{p}_{1}}{1 - {p}_{1}} - \dfrac{6{p}_{3}}{1 - {p}_{3}} = \dfrac{5{p}_{1}{p}_{3}}{\left(1 - {p}_{1}\right)\left(1 - {p}_{3}\right)}

⇒p1−6p3=0⇒ {p}_{1} - 6{p}_{3} = 0

⇒p1p3=6⇒ \dfrac{{p}_{1}}{{p}_{3}} = 6

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