|Jun2-12, 07:55 AM||#1|
[b]1. The problem statement, all variables and given/known data[
A stockpile of 40 relays contain 8 defective relays. If 5 relays are selected random, and the number of defective relays is known to be greater than 2, what is the probability that exactly four relays are defective?
2. Relevant equations
Calculus of probability
3. The attempt at a solution
I've been try to find the solution but I got confused. Can you guys help me?
This is my solution :
the probability from defective relays is : 8/40, the probability from 5 random is : 5/40 and the probability of 4 defective from 5 random select is : 4/5.
so my solution is ((5/40)/(8/40))x(4/5) = 25/32 =0.7815
is this right or my solution is wrong ..... thanks
|Jun2-12, 08:07 AM||#2|
Hi pluto31!! Welcome to physics forums!
Your solution is wrong. The question has already told you that the number of defective relays is known to be more than 2. Apply this condition to your solution, too
|Jun2-12, 04:02 PM||#3|
Now you have the problem of computing the [itex] p_i[/itex] for the relevant values of i. Can you see how to do that?
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