Full Q: A quality control engineer samples 5 from a large lot of manufactured firing pins and checks for defects. Unknown to the inspector, 3 of the 5 sampled firing pins are defective. The engineer will test the 5 pins in a randomly selected order until a defective is observed (in which the case the entire lot will be rejected). Let y be the number of firing pins the QC engineer must test. Find and graph the probability distribution of y,
My understanding: y should be 1, 2, and 3, since by the 3rd pin, the defect will definitely be it (if not on the first two) because of the 3/5 probability and sample size of 5. The prob that the first item drawn is a defect is p(y=1) = 3/5 -- this is correct.
For p(y=2) I figured (2/5)(3/) -- wrong! same for p(y=3)...
The answers given are: p(2)=3/10 , p(3)=1/10
I don't understand how......
2006-09-24
18:26:09
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2 answers
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asked by
Gizmo
1
in
Science & Mathematics
➔ Mathematics
....mmh, conditional prob didn't work or may be I didn't do it right.
Here's my new interpretation:
p(y=2)=p(2nd pin is the first defect)=(1/2!)(3/5) = 3/10
=> 1 = only one way to get 2nd pin as defect, 2! = Number of possible selections
=> 3/5 = probability of defect in total sample
p(y=3)=p(3rd pin is the first defect)=(1/3!)(3/5) = 1/10
... same rationale
Am I on the right path?
2006-09-24
19:32:24 ·
update #1