Answer:
0
Step-by-step explanation:
From the given information;
Let x be the number of trails on which the [tex]r^{th}[/tex] defective occurs.
Let the probability that an occurrence of a defective be p = 0.10
Suppose x is a random variable that follows a negative binomial distribution with parameters r and p.
Then the probability mass function of X can be expressed as:
[tex]P(X=x) = \bigg (^{x-1}_{r-1} \bigg)p^r (1 - p) ^{x-r} \ \ \ \ ; x=r, \ r+1 , \ r+2 , ...[/tex]
[tex]P(X=x) = \bigg (^{x-1}_{r-1} \bigg)(0.10)^r (1 - 0.10) ^{x-r}[/tex]
[tex]P(X=x) = \bigg (^{x-1}_{r-1} \bigg)(0.10)^r ( 0.90) ^{x-r} \ \ ... \ \ (1)[/tex]
We are to find the probability of the fourth defective engine will be found on the second trial.
i.e. r = 4 and x = 2
[tex]P(X=2) = \bigg (^{2-1}_{4-1} \bigg)(0.10)^4 ( 0.90) ^{2-4}[/tex]
[tex]P(X=2) = \bigg (^1}_{3} \bigg)(0.10)^4 ( 0.90) ^{-2}[/tex]
[tex]P(X=2) = \bigg (\dfrac{1!}{3!(1-3)!} \bigg)(0.10)^4 ( 0.90) ^{-2}[/tex]
[tex]\mathbf{P(X=2) = 0}[/tex]
