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# Forum: Probability

Probability course and homework discussion. Probability distributions. Probability theory, stochastic processes

1. ### Sticky: We only provide homework help to those who show effort

Welcome to Talk Stats Forum. In order to keep homework help effective and efficient, we request all members to abide by these guidelines: 1)...

• Replies: 0
• Views: 30,397
09-30-2005, 09:44 AM
1. ### Finding joint density

Let Y1 ~ N(1,3) & Y2~N(2,5) be independent random variables. Find the joint density of W1 and W2 if W1 = Y1 +2Y2 and W2=4Y1-Y2. How should I...

• Replies: 2
• Views: 2,738
02-01-2011, 12:14 PM
2. ### If a RV is a function of another RV, then they are dependent?

Hello all! This is my first post on this forum. I just have a simple question. If a rv Z is a function of another rv X, then is it guaranteed that...

• Replies: 6
• Views: 1,943
02-26-2013, 04:43 AM
3. ### Simple Probability Question

Hello everyone, I am having problem with a question: A manufacturer has 100 memory chips in stock, 4% of which are likely to be defective based on...

• Replies: 1
• Views: 2,549
BGM
02-26-2013, 12:27 AM
4. ### Average Probablities over a quarter

Hi all, I have the following probability data for a medical event, I need to find what was the overall probability for these three month? 1-...

• Replies: 1
• Views: 2,464
10-31-2016, 01:48 PM
5. ### Decisions: probabilities and preferences

Hello everybody. I was wondering if anyone could help me with the following problem. I need to decide between three options: a) spend my holiday...

• Replies: 2
• Views: 1,692
12-24-2012, 06:27 PM
6. ### Consistent Estimator

I'm new here so i'm not sure what is wrong with my tex (i cant get +)so I will write the correct information under my tex lines A balanced one way...

• Replies: 4
• Views: 6,263
alf
11-09-2011, 11:41 AM
7. ### Monte carlo conditioning

I am trying to learn how to reduce variance with conditioning. page 15 in these lecture notes: http://www.columbia.edu/~mh2078/MCS_Var_Red1.pdf ...

• Replies: 13
• Views: 3,061
alf
11-26-2011, 10:43 AM
8. ### Negativ Binomial distribution

I am trying to count number of occurrence for variable X. I have considered X as Poisson distributed since this sounds like a Poisson process. But...

• Replies: 2
• Views: 2,095
02-15-2015, 06:15 AM
9. ### Collect answers and determine probability

Hello! I'm trying to figure out a method to predict the most probable answer taking into account previous answers collected in a database. ...

• Replies: 0
• Views: 1,305
03-22-2012, 12:10 PM
10. ### Can anyone explain me the solution of this exercise please?

Hi i've found this exercise but I do not understand the solution: _________________________________________________________________ In a party c...

• Replies: 2
• Views: 1,578
04-30-2013, 05:52 AM
11. ### Can anyone help me with this exercise?

Hi! I have to do this exercise: Define a finite probabilistic Space (Ω; Pr) and 2 events A,B⊆ Ω and Pr ≠ Pr so that we can verify that ...

• Replies: 1
• Views: 1,907
BGM
04-30-2013, 09:10 AM
12. ### Use a tree diagram to calculate the probability

Hi everybody! I have to solve this exercise. We observe a tournament of 2 ^ n players, which consists of n rounds. In each round every 2 players...

• Replies: 0
• Views: 2,097
05-03-2013, 09:41 AM
13. ### Density of a random variable

Professor Roberto has to take an oral examination. The grading scale is as follows: 5: = best and 1: = worst. At most he only gives the note 4. Each...

• Replies: 2
• Views: 1,686
04-30-2013, 09:22 AM
14. ### Calculate the Expected value,Variance,density and 2nd moment

I have to solve this exercise. Here are also my solutions but I don't know if they're correct. Let Ω ⊆ R ^ 2 a finite set of points in R ^ 2....

• Replies: 3
• Views: 1,595
BGM
05-04-2013, 08:04 AM
15. ### Property of independent random variables

hello! I'm trying to understand the following property: Let X and Y be independent random variables z: = X + Y. Then where fZ (z) is the...

• Replies: 3
• Views: 1,720
06-21-2013, 11:36 AM
16. ### Multiplication Theorem on Probability and proof

Hi Everyone! I'm with Conditional Probability and I don't understan this theorem. Theorem: If then Proof:

• Replies: 1
• Views: 6,132
06-22-2013, 11:22 AM
17. ### Binomial Distribution Analysis Question

Hi everyone. I have a couple of questions and would greatly appreciate it if you could help me out! First, I'll provide some information: ...

• Replies: 4
• Views: 11,653
07-07-2012, 12:07 PM
18. ### Find the constant that makes f(x,y) a probability density function

Let X and Y have a joint density function given by f(x,y) =e^(-kX), 0<=X<inf, 0<=Y<=1, k is a constant, and 0 elsewhere Find the value...

• Replies: 12
• Views: 7,881
10-05-2011, 09:36 PM
19. ### Third Moment about the mean

Let E=μ4 S=/σ^3, where E(X-μ)^3=E(X^3)-3+2^3 How can I rewrite the right hand side of the above expression in terms of μ, σ^2, S and μ4. ...

• Replies: 11
• Views: 8,777
BGM
10-17-2011, 12:06 AM
20. ### Μarginal Distributions of f(x,y)

f(x,y) = e^(-x), 0<=x<inf, 0<=y<=1 To find the marginal PDFs here is what I did so far: Marginal Distribution of x: f(x) = integral...

• Replies: 2
• Views: 123,216
10-16-2011, 12:42 PM
21. ### Expected value of Yi^2

Yi is i.i.d. N(0,σ^2) for i=1 to n. E=0, var=σ^2 Show that E = 1 if E = 0, how does the the sum of squared Yi's equal 1?

• Replies: 3
• Views: 5,622
BGM
10-16-2011, 11:48 PM
22. ### Express E[X-μ]^4 in terms of....

X is a random variable with moments E, E, E. Suppose var(X)= σ^2, skewness is given as S=/(σ^3). Express the right side of the following as in...

• Replies: 0
• Views: 132,874
10-16-2011, 10:52 PM
23. ### show that the sum of e(i) = 0 and the sum of e(i)*Yhat(i) = 0

Consider a usual multiple linear regression model: Y = X β + ε where Y is a (n x 1) response vector, X is a (n x p) matrix with its first column...

• Replies: 16
• Views: 14,616
BGM
11-14-2011, 02:40 AM
24. ### Find the sample size

Given info: cost1=\$4, σ1=10, W1=N1/N=0.4 cost2=\$9, σ2=20, W2=N2/N=0.6 The first part of this question asks for the values of n1/n and n2/n that...

• Replies: 0
• Views: 1,408
02-05-2012, 05:08 PM
25. ### Bias of ratio estimator of pop.mean, DOUBLE POST

I need to explain why the ratio estimator of the population mean is biased or unbiased. I am fairly certain that it is a biased estimator but I don't...

• Replies: 0
• Views: 2,312
03-05-2012, 12:29 AM
26. ### Regression through origin, R^2=0

A 2-variable regresssion with no intercept is given as: Yi=β1Xi +ui, show that r-squared for this model is equal to zero. I know that R^2...

• Replies: 1
• Views: 1,512
10-21-2012, 09:59 PM
27. ### Linear Estimators help

Let x1, x2, x3, x4, x5 be a random sample where each of these observations are independent, E=...=E = μ; Var(x1)=...=Var(x5) = σ^2. μ1hat = x1 -...

• Replies: 1
• Views: 1,820
BGM
10-25-2012, 12:31 PM
28. ### Covariance of a linear comb. of independent variables

U = y1 - 2y2 + y3 W = 3y1 + y2 E = 1, E = 2, E = -1, Var = 1, Var = 3, Var = 5 Var(U) = 12, Var(W) = 12 ;I hope y1, y2, y3 are Independent RV's...

• Replies: 2
• Views: 1,759
10-18-2012, 10:48 PM
29. ### R^2=0

How can I show that R^2 can be equal to or less than zero? I can't find an example.

• Replies: 8
• Views: 2,198
11-02-2012, 12:48 AM
30. ### Variance of Marginal effects

I am trying to find Var(β3+xβ4+xβ5) where the x's are ages (20,30,40,50,55) The Marginal Function is: 14.09616 - 0.47037AGE + 0.0042AGE^2 I just...

• Replies: 4
• Views: 2,745
11-22-2012, 11:17 PM
31. ### Having trouble with an expected value manipulation

I'm having a little trouble with part a. Okay, okay, I'm having trouble with all of it, but I'm guessing that solving a will help with the rest....

• Replies: 5
• Views: 2,753
01-31-2013, 10:54 PM
32. ### On Correlation Matrices

Hi. This is a question from a question bank. I am self-studying for upcoming MS exam. a)Random vector X, elements are independent and zero mean....

• Replies: 6
• Views: 2,225
03-02-2012, 12:16 AM
33. ### Convergence in probability

Hi, Can you please help me with the following question? Any hints, ideas would be much appreciated. Suppose that the sequence Xn converges to...

• Replies: 4
• Views: 4,974
09-26-2007, 09:29 AM
34. ### identifying the distribution of a data set

Dear all I am creating a software that is reading tcp packets from a link. I have the following information available: size of the packet: ...

• Replies: 4
• Views: 5,279
08-16-2006, 10:58 PM
35. ### Probability problem

I am stuck, kindly help. There are two men V1 and V2. Each man has two buckets A and B. Bucket A contains numbered blocks from 7 to 14. Bucket B...

• Replies: 3
• Views: 1,446
03-20-2015, 08:33 AM

Just can't get my head around this question and it's killing me. Any bit of help would be amazing! thank you :) In a Jackpot Lottery, 1500 numbers...

• Replies: 0
• Views: 1,346
03-29-2012, 07:33 PM
37. ### Bayesian inference -(unknown mean and variance | and a proof)

hello, i take a bayes lesson. there are 3 questions as my homework, i did one of them. i am new to statistics, so instructor said i can get help as...

• Replies: 4
• Views: 5,105
10-22-2010, 05:07 PM
38. ### Help...

I'm not sure how to set up this binomial probability problem. I hope there is a good probability that someone can point me in the right direction. ...

• Replies: 4
• Views: 6,157
10-09-2012, 09:55 PM
39. ### probability

I'm very confused on where to start on my statistics project. I need help please. It says: "a woman has her purse stolen in LA by a young blonde...

• Replies: 1
• Views: 2,915
12-05-2006, 09:25 AM
40. ### condition expectation and variance

Let X, Y be independent exponential random variables with means 1 and 2 respectively. Let Z = 1, if X < Y Z = 0, otherwise Find E(X|Z) and...

• Replies: 0
• Views: 2,675
01-25-2008, 11:10 PM
41. ### pdf for a statistic describing N independent normal variates

I apologize in advance if this question has been asked before. One problem I have is in phrasing the question. Once I know the right language to...

• Replies: 0
• Views: 1,837
01-19-2009, 03:07 AM
42. ### something ANOVA-like?

I apologize for re-posting this question. I posted it a month ago in the probability forum, and after more than 100 views, there was no response...

• Replies: 1
• Views: 2,070
03-01-2009, 09:42 PM
43. ### Comparing probability distributions over discrete random variables

Hi guys Sorry if the post is not in the right place but I am new here. I am comparing the performance of two monte carlo methods. The results I...

• Replies: 0
• Views: 2,998
05-08-2011, 07:38 AM
44. ### Multi-choice, out of time

Hi In a multi-choice test with four answers each, I answer the first 75% but run out of time for the rest. In the few minutes left which is the best...

• Replies: 4
• Views: 1,892
03-14-2013, 09:20 PM
45. ### random walk

maybe you can help me... i've a theoretical problem: let X_n be a random walk over Z defined by For l,m in Z let

• Replies: 1
• Views: 3,884
12-19-2006, 05:01 AM
46. ### Bayes Theorem - JohnM vs my textbook

To JohnM or anyone who knows... I am struggling with positive and negative predictive values (PPV and NPV) homework problems. My textbook...

• Replies: 2
• Views: 3,003
09-10-2006, 08:27 PM
47. ### Help!!

I have been trying to figure this problem out...I know it is probably the easiest thing, but I just can't put my finger on it.... If anyone could...

• Replies: 1
• Views: 1,722
10-11-2006, 08:40 AM
48. ### incremental Mutual information

I computed Mutual information between two variables X and Y from data D at time t. I(X,Y) from D. Now at time t+1 new data arrived so, how i...

• Replies: 0
• Views: 1,683
03-15-2012, 05:53 PM

I'm having a tough time with my online stat course. Very limited feedback from instructor and I feel somewhat on my own. Can someone assist with...

• Replies: 1
• Views: 1,255
11-04-2014, 12:56 PM
50. ### Probability that a number in a group of numbers to be less than the average of group

Hi, I am new to probability and would like to know how to find the probability that a number in a group of numbers is less than the average of that...

• Replies: 2
• Views: 4,832
05-19-2008, 07:12 PM
51. ### sample size for a probit analysis

Hi there, I am conducting a hydrocarbon toxicity research using mosquito larvae as target. The idea of this research is to estimate the relative...

• Replies: 0
• Views: 4,547
07-07-2010, 06:08 PM
52. ### finding non-randomness in binomial successes?

Hi, I've only had one semester of Stats, so this is probably a real newbie question. I'm having problems on deciding how to approach a specific...

• Replies: 7
• Views: 3,309
01-04-2006, 08:04 AM
53. ### URGENT help needed

A company are searching for 5 oil wells in a landscape the sucess rate of finding a hole is 10% (0.1) for each hole therefore failure must be 90%...

• Replies: 1
• Views: 2,050
05-02-2007, 09:50 AM

A coin is tossed n times, where n is an odd number. Let X be the number of times heads show up in the n tosses. Define Y in terms of X as follows: if...

• Replies: 5
• Views: 2,709
BGM
05-09-2011, 11:55 AM
55. ### Expected Value of (1/N)

Someone rolls a pair of dice repeatedly until the first time a sum of eleven shows. Let N be the number of rolls required. Find E(1/N). So N is a...

• Replies: 2
• Views: 5,544
BGM
05-10-2011, 04:26 AM
56. ### A box contains 5 tickets

A box contains fives tickets, each with a letter on it: Box : S T A R T Once a day, for n days, a ticket will be drawn at random, with...

• Replies: 1
• Views: 3,002
BGM
05-10-2011, 04:35 AM
57. ### Uniform Distribution/Probability Density Function

I'm experiencing a mental block with this concept. If anyone could help me out, I'd be most appreciative. I understand the formula for the...

• Replies: 3
• Views: 9,956
11-29-2005, 09:29 PM

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