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having trouble with probability

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Bri MT:

--- Quote from: annaoh_2003 on January 20, 2022, 09:32:37 pm --- Im having issues with the symbols. can someone refer me to some good pages for this kind of stuff?

--- End quote ---

Assuming you're talking about understanding the maths notation fun_jirachi used, I'm not sure about a good page for it but Pr(A|B) means probability of A given B.
I.e. Pr(X=2|X>1) means probability that X is exactly 2 given that we know it as greater than one.

Hope this helps :)

annaoh_2003:
I tried doing this question
"A company produces 1000 refrigerators in a week at three plants. Plant A produces
350 refrigerators, plant B produces 250 refrigerators and plant C produces 400 refrig-
erators. Production records indicate that 5% of the refrigerators produced at plant
A will be defective, 3% of the refrigerators produced at plant B will be defective and
7% of the refrigerators produced at plant C will be defective. All the refrigerators
are shipped to a central warehouse.
If a refrigerator at the warehouse is found to be defective, what is the probability
that it was produced at plant A? "

I attached my page of working - is that how I do it?? do I just leave it as that fraction?? the question is 3 marks so I feel like im missing something...

wingdings2791:

--- Quote from: annaoh_2003 on January 20, 2022, 09:32:37 pm ---Im having issues with the symbols. can someone refer me to some good pages for this kind of stuff?

--- End quote ---

If you're having trouble typing the symbols, there is an excellent guide for LaTex on AN, found here! There are many PDFs available online that detail the code for the less common symbols should you need them.

Your working for this refrigerator question looks great- just be wary that the probability you are finding is \(Pr(A|D)=\frac{Pr(A \cap D)}{Pr(D)}\). You've got the correct formula and figures already (17.5/53), so just be mindful of using the right notation too to secure full marks. If the question doesn't specify an answer format, it's probably best to leave it as a fraction to avoid approximation. Hope this helps :)

annaoh_2003:

--- Quote from: wingdings2791 on January 22, 2022, 09:47:12 am ---If you're having trouble typing the symbols, there is an excellent guide for LaTex on AN, found here! There are many PDFs available online that detail the code for the less common symbols should you need them.

Your working for this refrigerator question looks great- just be wary that the probability you are finding is \(Pr(A|D)=\frac{Pr(A \cap D)}{Pr(D)}\). You've got the correct formula and figures already (17.5/53), so just be mindful of using the right notation too to secure full marks. If the question doesn't specify an answer format, it's probably best to leave it as a fraction to avoid approximation. Hope this helps :)

--- End quote ---

thanks ! so Pr(A|D) means probability of A given D- is D the event that 53 of the 1000 fridges are defective? Then what is A? cant be the event that the defective fridge is from plant A bc that event is Pr(A|D)?

fun_jirachi:
As it is described by wingdings, P(A) is the probability that a refrigerator was produced at plant A, irrespective of if it actually works or not.

"is D the event that 53 of the 1000 fridges are defective?" -- no it isn't. This is an oddly worded event too, and in any case, the probability of this event would be one since we're given in the question that 53 are defective. P(D) is the probability that a particular refrigerator is defective ie. the chance that we get a defective one if we pick one of the thousand at random.

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