Probability 5 Question 11

11. One hundred identical coins, each with probability p, of showing up heads are tossed once. If 0<p<1 and the probability of heads showing on 50 coins is equal to that of heads showing on 51 coins, then the value of p is

(1988, 2M)

(a) 1/2

(b) 49/101

(c) 50/101

(d) 51/101

Fill in the Blanks

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Answer:

Correct Answer: 11. (d)

Solution:

  1. Let X be the number of coins showing heads. Let X be a binomial variate with parameters n=100 and p.

Since,

P(X=50)=P(X=51)

100C50p50(1p)50=100C51(p)51(1p)49(100)!(50!)(50!)(51!)×(49!)100!=p1pp1p=5150p=51101



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