Ten percent of the engines manufactured on an assembly line are defective. If engines are randomly selected one at a time and tested, what is the probability the fourth defective engine will be found on the second trial?

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Step-by-step explanation:

From the given information;

Let x be the number of trails on which the 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:

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