• Support PF! Buy your school textbooks, materials and every day products Here!

Binomial Probability problem.

  • #1

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.

Homework Statement





Homework Equations





The Attempt at a Solution

 

Answers and Replies

  • #2
tiny-tim
Science Advisor
Homework Helper
25,832
251
Hi TheHamburgler1! :smile:

No, it's just P(first is defective is the 5th) + … + P(first is defective is the 25th) :wink:
 
  • #3
Hi TheHamburgler1! :smile:

No, it's just P(first is defective is the 5th) + … + P(first is defective is the 25th) :wink:
Would we not express each of those via Bin(n,.1) where x=1? If not, how would we express one of them?

Thanks
 
  • #4
Actually, this could be a Geometric distribution problem right? In that case we would sum x from 5 to 25 of (.1)(.9)^(x-1). This gives 0.5843102
 
  • #5
tiny-tim
Science Advisor
Homework Helper
25,832
251
(just got up :zzz: …)
Actually, this could be a Geometric distribution problem right? In that case we would sum x from 5 to 25 of (.1)(.9)^(x-1).
Yup! :biggrin:

(and I assume you've used algebra to calculate that, and not 20 additions? :wink:)
 

Related Threads on Binomial Probability problem.

Replies
2
Views
983
Replies
1
Views
1K
Replies
3
Views
2K
  • Last Post
Replies
2
Views
1K
Replies
1
Views
2K
  • Last Post
Replies
2
Views
740
  • Last Post
Replies
6
Views
6K
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
1
Views
935
  • Last Post
Replies
14
Views
5K
Top