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## Homework Statement

10% of engines manufactured on an assembly line are defective. If engines are randomly selected one at a time and tested, what is the probability that the first defective engine will be found between the 5th trial and the 25th trial, inclusive?

## Homework Equations

## The Attempt at a Solution

I believe this is just a binomial distribution with Bin(n,1) where n varies between 5 and 25.

[tex]\sum[/tex](nC1)(0.1)(.9)^(n-1)

This is way off because I am getting 6.47...

thanks ahead of time.