# Search results

1. ### Statistics Question -> Elevator Question

I don't really know how to phrase this question. But what floor in a building takes the less time to wait for an elevator? Like for example. Say that there's a building with two elevators in it. Each floors are the same height. Each elevator travels at the same speed. The first floor has...
2. ### Probability Weibull Distribution

Homework Statement Suppose that x has a Weibull distribution with parameters \alpha and \beta and that P(x \leq 1)=.105 and P(2 \leq x)=.641. What are \alpha and \beta? Homework Equations F(x) = 1 - e^{-(\frac{x}{\beta})^{\alpha}} The Attempt at a Solution When I try and solve...
3. ### Probability Question - Urn problem

oh i guess i always assumed you pick the things simultaneously as that's what I've been doing throughout the course so i guess this assumption is wrong?
4. ### Probability Question - Urn problem

Homework Statement An urn contains 4 white and 4 black balls. We randomly choose 4 balls. IF 2 of them are white and 2 are black, we stop. If not, we replace the balls in the urn and again randomly select 4 balls. this continues until exactly 2 of the 4 chosen are white. What is the...
5. ### Probability Question - Exponential Distribution

oh thanks i missed that
6. ### Probability Question - Exponential Distribution

Homework Statement Suppose that X has an exponential distribution with mean μ. Find the probability that x lies within one standard deviation of its mean, that is find P(μ-σ≤X≤μ+σ) Homework Equations The Attempt at a Solution If I'm not mistaken the standard deviation is equal...
7. ### Probability Question

Using the definition $$E[x] = ∫^{\infty}_{-\infty} x f_{x}(x)\, dx$$ So in the case of raising to a power $$E[x^{n}]=∫^{\infty}_{-\infty} x^{n} f_{x}(x)\, dx$$ We are given that $$f_{x}(x) = \begin{cases} kx^{2} & \text{for }-1 \leq x \leq 1 \\ 0 & \text{otherwise} \end{cases}$$ In...
8. ### Probability Question

Homework Statement Suppose that X has pdf f(x) = kx^{2} for -1\leq x \leq 1, 0 otherwise (a) What is k? (b) What is Ex^{n} where n\geq 0 is an odd integer? (c) What is Ex^{n} where n\geq 0 is an even integer? Homework Equations The Attempt at a Solution For (a) I get 1.5...
9. ### Probability Question

What am I doing wrong though? I can't seem to find what it is exactly that I am doing wrong.
10. ### Probability Question

So now that I think of it using the information you provided \frac{1}{n+1}\sum^{n+1}_{X'=1}X'=\frac{1}{n+1}\sum [1 + 2 + 3 + ... + n+1] = \frac{1}{n+1}(1+[1+ 2+ 3 + ... + n]) = \frac{1}{n+1}(1+\frac{1}{2}n(n+1))=\frac{1}{n+1}+.5 n I still get the same answer
11. ### Probability Question

But I want to sum to n+1 and not n. How does this effect the answer? I haven't taken calculus 2 in several semesters. I remember some change of base thing. \sum^{n+1}_{X'=1}X'=\sum^{n}_{X'=0}(X'-1) Is this correct?
12. ### Probability Question

Homework Statement Random variable X takes values a,a+Δ,a+2Δ,...,a+nΔ with equal probabilities. (a) What is Ex? (b) What is Var X? Homework Equations The Attempt at a Solution X = [a,a+Δ,a+2Δ,...,a+nΔ] X = a+(X'-1)Δ where X' is some random variable X' = [1,2,...,n+1] I test to make sure...
13. ### Probability Question - Ball Urn Problem

So given the question how do you know if there's replacement or not?
14. ### Probability Question - Ball Urn Problem

Why is that? If you draw a Red ball on the first than there's no way to draw two white balls.
15. ### Probability Question - Ball Urn Problem

Well what if you don't know if the first ball is drawn is W or or G? 1/7 if you draw W on the first draw but if you draw R on the first than the probability you draw two W is zero so how would you answer this question then since there are two answers I guess?
16. ### Probability Question - Ball Urn Problem

Using the binomial theorem you can solve ball urn problems. Like say for example a urn has 4 green balls and 3 white balls. You draw two balls. What's the probability you draw 2 white balls? I just made this problem up off the top of my head. But anyways using the binomial theorem...
17. ### Probability Question

P(A intersection B) = P(A)P(B) not sure what to do from here because it's conditional probabilities.
18. ### Probability Question

Ok sorry about that I fixed that. Thanks for helping me.
19. ### Probability Question

Homework Statement Suppose P(A|B) = P(A|B^c) (P(B) > 0 and P(B^c) > 0 both understood). Show that A and B are independent. Homework Equations The Attempt at a Solution I don't know where to go from here. Thanks for any help \frac{P(A \bigcap B)}{P(B)} = \frac{P(A \bigcap B^{c})}{P(B^{c})}
20. ### Probability Question - Prove Formula

I think I actually figured this one. I realize that A, B, C may not necessairly be independent and for whatever reason I thought they where so I wasn't getting the correct answer
21. ### Probability Question - colored balls in 2 bowls - Baye's formula?

Ok so I figured out my mathematical miscalculation in A and was able to figure out the answer to B (I realized I forgot to post it). What is that symbol mean? ¬?
22. ### Probability Question - Prove Formula

Homework Statement Hi, Prove P(AUB|C) = P(A|C)+P(B|C)-P(A∩B|C) Homework Equations The Attempt at a Solution I start off from here P(AUB|C)=\frac{P(AUB)P(C|AUB)}{P(C)} I don't know where to go from here. Thanks for any help that you can provide.
23. ### Probability Question - colored balls in 2 bowls - Baye's formula?

Is it just (1/2)(3/4) for part A?
24. ### Probability Question - colored balls in 2 bowls - Baye's formula?

Probability Question -- colored balls in 2 bowls -- Baye's formula? Bowl #1 contains 2 red balls and 2 white balls Bowl #2 contains 3 red balls and 2 white ball one bowl is chosen at random (each is equally likely) (A) What is the probability of choosing a red ball? Let R stand for...
25. ### Probability Question - using the combinations counting form C(n,k)

Oh ok thanks I got it
26. ### Probability Question - using the combinations counting form C(n,k)

I guess it's simply 1/C(12,3)? I'm not sure how to solve (b) though
27. ### Probability Question - using the combinations counting form C(n,k)

Probability Question -- using the combinations counting form C(n,k) Homework Statement 4. A bowl contains 3 red chips, 4 green chips, and 5 blue chips. A batch of 3 chips is withdrawn at random. (a) What is the probability that the batch contains only red chips? (b) What is the probability...
28. ### Conditional Probability Question

my answer is [C(n,2)*c(n,2)]/C(n,4) I was wondering if you can write C(n,2)*C(n,2) as C^2(n,2)?
29. ### Conditional Probability Question

Ya I guess your right about this. I don't know if I can do this notation but can I do (N_{K})^{2} Square N choose K in this notation? I have never seen this before don't see why I can't use this notation. I couldn't figure out how to do this in itex code
30. ### Conditional Probability Question

Homework Statement A population has n men and n women. If you where to take 4 people out of the population to form a group what's the probability that there are exactly the same number of men as women in the group . Homework Equations The Attempt at a Solution Ok so I thought...