Given is X ~ B (n, p). If E(X) = 6, and Var(X) = 4.2, find the value of n.

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#### Solution

Given E(X) = 6, Var (X) = 4.2

Now E(X)/V(X) =np/npq

6/4.2=1/q

q=4.2/6=0.7

since p+q=1

p+0.7=1

p=0.3

Now, E(X) = np

6 = n x 0.3

n=6/0.3=60/3

n=20

Concept: Bernoulli Trial - Calculation of Probabilities

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