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Question
Let X ~ B(10, 0.2). Find P(X = 1).
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Solution
X ~ B(10, 0.2)
∴ n = 10, p = 0.2
∴ q = 1 − p = 1 − 0.2 = 0.8
The p.m.f. of X is given by
P(X = x) = nCx px qn−x
∴ P(X = x) = 10Cx (0.2)x (0.8)10−x ...[x = 0, 1, 2, 3, ...., 10]
P(X = 1) = 10C1 (0.2)1 (0.8)10−1
P(X = 1) = 10 × (0.2) × (0.8)9
P(X = 1) = 2(0.8)9
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