Let a random variable X has a binomial distribution with mean 8 and variance 4. If P X ≤ 2 = k 2 16 , then the value of k is equal to

Question

Let a random variable X has a binomial distribution with mean 8 and variance 4. If P X ≤ 2 = k 2 16 , then the value of k is equal to, 121, 1, 17, 137

MARKS App · Accepted Answer

Let n be the number of times the experiment is done, p is the probability of success and q is the probability of failure ∴ n p = 8 (mean), n p q = 4 (variance) ⇒ q = 1 2 ⇒ p = 1 2 ⇒ n = 16 P X ≤ 2 = p X = 0 + p X = 1 + p X = 2 = 16 C 0 p 0 q 16 + 16 C 1 p 1 q 15 + 16 C 2 p 2 q 14 = 1 2 16 + 16 1 2 16 + 120 × 1 2 16 = 1 2 16 137 = 137 2 16 = k 2 16 ∴ k = 137

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