Question

Hi, my problem is the following: "a engines factory separate from its daily production line of 350 pieces a sample of 30 items for inspection. The number of defective pieces is 14/day. What's the probability that the sample contains at least 3 defective pieces?"
The exercise I've been doing points out that the correct answer is "0,108453", but what I find in any calculus I try is "0,9....". Can someone tell me where is my mistake?

Answer 1

at least 3 means not none, not one, not two
so computer those probabilities and subtract from one
are you supposed to use binomial probability?

Answer 2

\[\frac{14}{350}=\frac{1}{25}=.04\] if you are using binomial, probablity that none of the 30 are defective is
\[.96^{30}\]
probability one is defective is
\[30\times .96^{29}.04\] and probability two are defective is
\[\dbinom{30}{2}.96^{28}.4^2\] add these up and subtract from one

Answer 3

I've used binomial probability, but the answer was 0,9....

Answer 4

Tell me what you did find as result..

Answer 5

let me check it

Answer 6

http://www.wolframalpha.com/input/?i=1-%28.96%29^30-30*.96^29*.04-30+choose+2%28.96%29^28*.04^2

Answer 7

not quite what the book has, but i like my answer just fine

Answer 8

I've just found 0,1049, ignoring some digits. But it sounds plausible. :P Can you tell me why is it 14/350 instead of 14/30 if the sample is supposed to be 30?