<PRE><B>Question 1159301</B>
Look at 1000 from each machine

====Def======ND===Total
1-----50 -----    950---- 1000
2---- 30---------970-----1000
3-----40--------960----1000
4-----80--------920----1000
tot--200--------3800---4000

If defective (200) probability it came from machine 2 is 30/200 or 0.15
The probability it did not come from machine 2 is 0.85, the complement
If it is not defective (3800) the probability it was from machine 2 is 970/3800 or 0.255.
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