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# Show that E(X) = np when X is a binomial random variable. ISBN: 9780321629111 32

## Solution for problem 64E Chapter 3

Probability and Statistics for Engineers and the Scientists | 9th Edition

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Problem 64E

Show that E(X) = np when X is a binomial random variable. [Hint: First express E(X) as a sum with lower limit x = 1.Then factor out np, let y = x - 1 so that the sum is from y = 0 to y = n - 1, and show that the sum equals 1.]

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Problem 64E Answer: Step1: Let “X” be random variable it follows binomial distribution with parameters “p” and “n”. The probability mass function of binomial distribution is given by p(x) = C p q n-, x = 0,1,2,...,n x We need to prove mean E(x) = np. Step2: Consider, n E(X) = xP(X = x) x=0 n n x nx = x[( )px(1 p) ] x=0 n = x[ n! p (1 p) nx] x=0...

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##### ISBN: 9780321629111

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