A fair coin is continually flipped until heads appears for the 10th time. Let X denote the number of tails that occur. Compute the probability mass function of X.

Short Answer

Expert verified

In the given information the answer isP(X=x)=9+xx1210+x.

this distribution is well known as negative binomial distribution

Step by step solution

01

Step 1:Given Information

Probability of Head(p)=12Tail (q)=12

Suppose in10+Xtrials, there are 9 heads and remaining all are tails and the last ends with head.

The event can also be written as getting 9 heads from 9+Xtrials. since the trials are independent, the probability of head with parameters p and q.

02

Step 2:Calculation

P(X=x)=9+xx12x129+x-x12

=9+xx121012x

=9+xx121012x

localid="1646896188334" =9+xx1210+x

03

:Final Answer

The final answer isP(X=x)=9+xx1210+x

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