Let X be the number of Bernoulli (p) trials required to produce exactly 1 success and at least 1 failure. Find the distribution of X. How can I answer this question if I don't know how many trials have taken place?

Katelyn Reyes

Katelyn Reyes

Answered question

2022-08-11

The number of Bernoulli trials required to produce exactly 1 success and at least 1 failure.
Let X be the number of Bernoulli (p) trials required to produce exactly 1 success and at least 1 failure. Find the distribution of X.
How can I answer this question if I don't know how many trials have taken place?
For context, the section this comes from was about Poisson distribution.
( n k ) p k ( 1 p ) ( n k ) e μ μ k k !
as  n  and  p 0  with  n p = μ
However I read in a different book that you can use the Geometric probability model for Bernoulli trials: Geom(p)
P ( X = x ) = q X 1 P
where p is prob. of success, X is number of trials, and q is prob. of failure

Answer & Explanation

nedervdq3

nedervdq3

Beginner2022-08-12Added 13 answers

Step 1
The only posibilities for X ( since exactly one sucess is allowed)
x = 2 > { S F , F S } x = 3 > { F F S } x = 4 > { F F F S }
Step 2
If p = P ( S )
P ( X = 2 ) = 2. p . ( 1 p ) 1 p 2
P ( X = x ) = ( 1 p ) 2 . ( 1 p ) x 2 . p 1 p 2 = ( 1 p ) x . p 1 p 2     x 3
the denominator 1 p 2 is because you're not allowing the secuence SS

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