Probability 3 Question 37

37. A coin has probability p of showing head when tossed. It is tossed n times. Let pn denotes the probability that no two (or more) consecutive heads occur. Prove that p1=1, p2=1p2 and pn=(1p)pn1+p(1p)pn2,n3.

(2000,5M)

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Solution:

  1. Since, pn denotes the probability that no two (or more) consecutive heads occur.

pn denotes the probability that 1 or no head occur.

For n=1,p1=1 because in both cases we get less than two heads (H,T).

For n=2,p2=1p (two heads simultaneously occur).

=1p(HH)=1pp=1p2

For n3,pn=pn1(1p)+pn2(1p)p

pn=(1p)pn1+p(1p)pn2

Hence proved.



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