Q90 of 108 Page 271

Suppose a random variable X follows the binomial distribution with parameters n and p, where 0 < p < 1. If P(x = r) / P(x = n–r) is independent of n and r, then p equals

In binomial distribution, we know P(X=r) = nCr

where q=1-p


Therefore,


= nCr / nCr


= /


Since, nCr= nCn-r



Accorting to question, this expression is independent of n and r if



Hence, p =1/2

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