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Question

If the independent random variables X,Y are Binomially distributed with n = 3, p = \(\dfrac{1}{3}\)  and n = 5, p =  \(\dfrac{1}{3}\)  respectively, then the probability of (X + Y ≥ 1) is:

This question was previously asked in
SSC CGL 2018 (Tier 2) Statistics Previous Year Paper (22-feb-2018)
The correct answer is

1 - \((\dfrac{2}{3})^8\)

Step 1 — Use the additive property of independent Binomials with equal p:

If \(X \sim B(3, 1/3)\) and \(Y \sim B(5, 1/3)\) are independent, then \(Z = X+Y \sim B(8, 1/3)\).

Step 2 — Apply the complement rule:

\[P(Z \ge 1) = 1 - P(Z = 0)\]

Step 3 — Compute P(Z = 0):

\[P(Z=0) = \binom{8}{0}\left(\dfrac{1}{3}\right)^0\left(\dfrac{2}{3}\right)^8 = \left(\dfrac{2}{3}\right)^8\]

Therefore \(P(X+Y \ge 1) = 1 - \left(\dfrac{2}{3}\right)^8\).

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Important Questions from Binomial Distribution

  1. In a Binomial distribution, the mean is three times its variance. What is the probability of exactly 3 successes out of 5 trials?

  2. If mean and variance of a Binomial variate X are 2 and 1 respectively, then the probability that X takes a value greater than 1 is

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  5. If log e(x) is normally distributed with mean 1 and variance 4, then P(0.5 < x < 2) is:

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