# Thread: Probability - Hypergeometric random variable

1. ## Probability - Hypergeometric random variable

I am trying to help my child with her homework, and I don't have a clue how to answer this.

Four ball are randomly selected without replacement from an urn containing 20 balls numbered 1 - 20

1.A) Let Y denote the number of balls numbered 16 or higher. Determine the probabilty distribution ( probability mass function) of Y.

1.B) Use the probabilty mass function to determine the probability that the largest value in the selection is at most 15.

2.A) Let X equal the largest number in the selection. Is X hypergeometric?
2.B) Determine the probablity distribution (probability mass function) of X. Use this to determine the probability that the largest value is at most 15.

2. Originally Posted by PatCal
I am trying to help my child with her homework, and I don't have a clue how to answer this.

Four ball are randomly selected without replacement from an urn containing 20 balls numbered 1 - 20

1.A) Let Y denote the number of balls numbered 16 or higher. Determine the probabilty distribution ( probability mass function) of Y.

1.B) Use the probabilty mass function to determine the probability that the largest value in the selection is at most 15.

2.A) Let X equal the largest number in the selection. Is X hypergeometric?
2.B) Determine the probablity distribution (probability mass function) of X. Use this to determine the probability that the largest value is at most 15.

I will get you started:

Question 1

Using the notation found here: Hypergeometric distribution - Wikipedia, the free encyclopedia

Y ~ Hypergeometric(m = 5, N = 20, n = 4)

(a) Substitute the above values into the pmf given at the above link. Note that the support of Y (that is, the values that Y can have) is 0, 1, 2, 3, 4.

(b) The probability that the largest value in the selection is at most 15 will be Pr(Y = 0) (why?).

Question 1

(a) No.

(b) Calculate $\Pr(X \leq 15) = 1 - Pr(X > 15)$.

3. ## Probability - hypergeometric

Thank you for the reply, but I still do not understand.

PatCal

4. Originally Posted by PatCal
Thank you for the reply, but I still do not understand.

PatCal
What don't you understand? Please be specific.

5. ## Probability - hypergeometric variable

I am sorry, but I do not understand this question at all. I need to be walked through all the steps.

It has been 30 years since I did this sort of stuff, and it just isn't sticking .

PatCal

6. Originally Posted by PatCal
I am sorry, but I do not understand this question at all. I need to be walked through all the steps.

It has been 30 years since I did this sort of stuff, and it just isn't sticking .

PatCal