Recent content by eskimotaro

Fantastic! Then I guess I am done. Thank you so much for your help. Truly appreciate it. The Physics forums seems like a very interesting place, I think I will stick around and lurk. :)

What I mean is, the probability that 0 of 49 people with DNA type S not being in the database should be that same as what I am looking for? The probability that there is exactly one person with DNA type S, given that the contributor is in the database. Since I have already account for the 1...

Ah, that makes a lot of sense! Guess I misunderstood it. What do you think about my calculation for (e)? That's the probability that 0 of 49 are not in the database. Which is what the hint says that we're interested in. Is that what I am looking for?

Alright, I see. So I thought more about (e) based on what you said earlier and the hint. Using a hypergeometric formula, I calculated this: \frac{({49}\ C \ {0})*({4999950}\ C \ {29999})}{({4999999}\ C \ {29999})} Which \approx 0.7446 That's the probability that 0 of the 49 left are in the...

But you're saying that the answer isn't \frac{1}{50} either? Given that there is exactly one person with DNA type S in the database, and knowing that there are 50 individuals with type S, the probability that the individual with matching DNA is the culprit is \frac{1}{50}? EDIT: Or do you say...

If there's is exactly one person with DNA type S in the database, then the probability of picking that person is \frac{1}{30000}. That's the answer then I believe? Is that also what you are hinting at? P(A | X = 1) = \frac{1}{30000} Will have to think more about this one.

This one is simply \frac{1}{50}. But I'm not sure what to do with that. This presupposes that I am already choosing among the ones I know have DNS type S. Or is that exactly the meaning of P(A | X = 1)? EDIT: P(A | X = 1) is the probability that the criminal is chosen, given that we are already...

Is this for the (e) or (f) question? I'm sorry the language confuses me sometimes. EDIT: Should I try to figure our the probability that 49 samples in the database are not type S? Can I use: P(S^{c}) = 1 - \frac{50}{5000000} somehow?

I think I have thought too much about this problem lately, I'm not sure if what I did above even is correct. But it does make sense I think. I'm thinking P( A \mid X = 1) = \frac{P(X = 1 \mid A)*P(A)}{P(X = 1 \mid A)*P(A) + P(X = 1 \mid A^{c})*P(A^{c})} Then I need to find P(X = 1 \mid...

Then it doesn't seem like there's much of a difference between P(X = 1 | A) and P(X = 1). Would you say that's correct? Scratch that I wrote before your edit. Ah, of course. So instead I should look for the probability of there being 0, but with the numbers excluding the 1 criminal...

Oh, do you suggest I use the hypergeometric or binomial formula again? So if I use a binomial formula with p = 49/4999999 and n = 29999 I get the following: 29999*(\frac{49}{4999999})^{1}*\left(1-\frac{49}{4999999}\right)^{29999-1} Which equals about 0.22 again.

Gotta admit I'm sort of lost here. So if we have 49 persons with DNA S in a population of 4999999. What's the probability that none of them are among the 29999 left in the database? Should that be (4999999 - 29999) / 4999999? The hint says that we are somehow interested in the probability of...

Hmm. So if no one else in the database are to have the same DNA, then they can not be among the 50 that have S. But we have already included one. So there are 49 persons with S that need to be outside the database? That's 29999 left in the database, and we need to exclude 49? But the rest of...

Thank you for your reply. :) For (d) I guess the answer must be P(A) = 30000/5000000 = 3/500? Not sure about (e) though. P(X = 1 | A) means the randomly selected person has the DNA, given that he is a contributor? Does it mean the answer is 29999/4999999? The hint sort of confuses me.

Hello everyone. I have been given a problem in my Introductory Mathematical Statistics class. Been thinking about this one for a while and I am simply stuck. 1. Homework Statement "There has been found a DNA of type S on a crime scene. We will assume a total population of N = 5000000 that are...