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JEE Main 202118 MarchEvening Shift
Exam
JEE Main
Year
2021
Date
18 March
Shift
Evening Shift
Subject
Mathematics
Chapter
Probability

JEE Main 2021 · 18 March · Evening Shift · Mathematics · Probability

Let in a Binomial distribution, consisting of 5 independent trials,...

Let in a Binomial distribution, consisting of 55 independent trials, probabilities of exactly 11 and 22 successes be 0.40960 . 4096 and 0.20480 . 2048 respectively. Then the probability of getting exactly 33 successes is equal to :

Options

  1. A32625\dfrac{32}{625}
  2. B80243\dfrac{80}{243}
  3. C40243\dfrac{40}{243}
  4. D128625\dfrac{128}{625}

Correct answer

A. 32625\dfrac{32}{625}

Step-by-step solution

P(X=1)=C15⋅p.q4=0.4096P\left(X = 1\right) = C1 5 \cdot p . {q}^{4} = 0 . 4096

P(X=2)=C25⋅p2⋅q3=0.2048P\left(X = 2\right) = C2 5 \cdot {p}^{2} \cdot {q}^{3} = 0 . 2048

⇒q2p=2⇒ \dfrac{q}{2p} = 2

⇒q=4p⇒ q = 4p and p+q=1p + q = 1

⇒p=15⇒ p = \dfrac{1}{5} and q=45q = \dfrac{4}{5}

Now

P(X=3)=C35⋅(15)3⋅(45)2=10×16125×25=32625P\left(X = 3\right) = C3 5 \cdot {\left(\dfrac{1}{5}\right)}^{3} \cdot {\left(\dfrac{4}{5}\right)}^{2} = \dfrac{10 \times 16}{125 \times 25} = \dfrac{32}{625}

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