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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: 30,331
09-30-2005, 09:44 AM
1. ### Probability Question

I was given 10 problems is my stats class and is having an issue with one. Can someone help me? Suppose n men throw their hats into a pile and...

• Replies: 4
• Views: 2,600
11-26-2008, 09:02 AM
2. ### random variables and variance

if we let X be a (continous or discrete) random variable with range Rx how can we find Var(X)?? i dont have any clue plz help me. thx

• Replies: 4
• Views: 3,627
11-26-2008, 07:00 AM
3. ### Help. Have answer but teacher says wrong.

A study of 500 pastors in the Baptist Church found that their sermons lasted an average of 20 minutes with a standard deviation of 3 minutes. If a...

• Replies: 4
• Views: 2,812
12-09-2008, 03:03 PM
4. ### Moving window of Standard Deviation

I'm not sure how best to phrase this, so please bear with me: I have a stochastic process from which I can measure one representative value per...

• Replies: 4
• Views: 6,426
12-30-2008, 07:56 PM
5. ### how many combinations ?

4 numbers with each can be from 1 to 49. e.g. 1,2,3,4 1,2,3,5 1,2,3,6 1,2,3,7 but exclude depublication that is 2,1,3,4 or...

• Replies: 4
• Views: 3,954
01-29-2009, 10:02 PM
6. ### calculating expectation and variance

Hi, I wanted to know if i'm on the right track with this problem. So far, for expectation I multiply 15/60 and 12. Not sure if this is correct....

• Replies: 4
• Views: 5,138
02-01-2009, 02:17 PM
7. ### joint density, change of variables

Need help with understanding. Two independent points dropped randomly on the interval. What is the density function of their distance x-y. I tried...

• Replies: 4
• Views: 3,867
02-05-2009, 10:38 AM
8. ### conditional expectation and variance

Hi there, Suppose X~Exp(lam). We have a sample from X of size n. Knowing that the data follow the exponential diastribution, we fit the...

• Replies: 4
• Views: 4,678
02-09-2009, 01:54 PM

A college use two different textbooks during the last semester. During last semester 0.7 students used the text book by Professor B. and 0.3 students...

• Replies: 4
• Views: 4,799
02-18-2009, 12:56 AM
10. ### normal distribution problem

Question..?? I cant seem to get this right. Do I find the z-score then do the problem or... please help.. question The life span of oil-drilling...

• Replies: 4
• Views: 5,532
03-01-2009, 11:28 AM
11. ### MLE for iid sample

I am trying to find the MLE of theta where the pdf is f(x;theta)=theta.x^(n-1) and then show that its variance-->0 as n-->inf I have found the...

• Replies: 4
• Views: 3,634
03-25-2009, 02:20 AM
12. ### random numbers vs dice

Hi my stats knowledge is sufficient to think of this problem but insufficient to get the answer, and its annoying me! Assume I have 46656 base 6...

• Replies: 4
• Views: 4,469
12-28-2009, 12:30 AM
13. ### Poisson Distribution

Hi all, it's me again! Just got a quick question here with the poisson distribution. Suppose messages arrive at a voice mail system according to a...

• Replies: 4
• Views: 4,781
04-06-2009, 10:23 AM
14. ### probability from moment generating function?

if the moment generating of a random variable X is M_x(t)=(1-t)^-2 compute P(-2 < X < 3) or explain why it cannot be computed how do I do...

• Replies: 4
• Views: 6,571
04-10-2009, 08:27 AM
15. ### Poisson. Calculate expected frequency problem.

I've decided to brush up on my statistics recently by jumping right in the middle of it, and I landed on the normal distribution. I have this...

• Replies: 4
• Views: 10,357
06-15-2009, 09:07 AM
16. ### probability and the normal curve

I am in grad school getting a master's in education. I am currently enrolled in a stats class and I am not too good at math and definitely not stats....

• Replies: 4
• Views: 4,910
06-24-2009, 07:55 PM
17. ### Expected Value of pmf

I am currently preparing for my upcoming actuary p/1 exam. The following question was in an book I am using:...

• Replies: 4
• Views: 11,966
06-26-2009, 04:09 PM
18. ### Problem involving pdf

Let X be the random variable which measures how long a light bulb lasts. If the probability density function of X is given by: f(X) = C/(x^3) ; x...

• Replies: 4
• Views: 2,125
07-12-2009, 12:49 AM
19. ### Probability of events occuring at the same time?

Hi! I'm having a bit of trouble calculating a probability as my statistics are a little bit rusty. Basically, I have 25 independant Wireless G...

• Replies: 4
• Views: 5,903
07-24-2009, 11:24 AM
20. ### Need Solution Verified!

Question: The income of junior executives in a large corporation are normally distributed with a standard deviation of \$2000. A cutback is pending,...

• Replies: 4
• Views: 2,796
08-25-2009, 01:38 PM
21. ### Normal Distribution and Z-Score Help

I am working on a problem and I am having problems with the z-score I calculate. The problem is: A baseball player's average distance is 180...

• Replies: 4
• Views: 4,032
09-22-2009, 02:26 PM
22. ### Help, suspiciously common birthdate

I have a database with 41469 medical practice patients. The patients have 22499 different (unique) dates of birth. Sorting by occurrence produces...

• Replies: 4
• Views: 2,567
09-27-2009, 02:23 AM
23. ### Probability in the Design of Social Games

Hey all, I have a math major and in my free time I design online social games. Frequently in these games, players are divided into groups and often I...

• Replies: 4
• Views: 3,122
BGM
09-27-2009, 01:04 AM
24. ### conditional expected value #2

I have two possibilities; X1 and X2. I set up a table: X2: 2: 0: -2 : X1: 0 : 0.1 0.2 0.1 -2: 0.0 0.3 0.3 Then I found: Px1(0)...

• Replies: 4
• Views: 2,971
BGM
09-27-2009, 10:57 AM
25. ### probability problem

I have a probability problem that is confusing me i think over a fine point taht i'm not getting. Here is the problem: a pizza with 8 slices,...

• Replies: 4
• Views: 2,347
BGM
09-27-2009, 12:47 AM
26. ### Density function?

Please can you help me solve this the pdf of continues r.v. X where f(x) {(2x 0≤x≤1 0 elsewhere} 1)...

• Replies: 4
• Views: 3,188
10-05-2009, 04:09 PM
27. ### Simple Probability Question... That I Don't Understand

I am attempting to do some online homework but I'm stuck on the very first question. The first bit wasn't too hard to figure out (I merely multiplied...

• Replies: 4
• Views: 7,026
10-04-2009, 08:48 PM
28. ### Simple probability question. Involves drawing name for gift.

We had a dinner with my family where we draw names to give gift this christmas. The only rule was to not pick our name. We did it a couple of time...

• Replies: 4
• Views: 5,514
10-14-2009, 10:08 PM
29. ### probability problem

Hi, i'm currently taking intro stats in college and I'm having trouble with probability questions. Here's one of the questions I'm working on: ...

• Replies: 4
• Views: 2,401
10-12-2009, 10:56 AM
30. ### Help!!! Normal distribution probability problem..

I don't know if anyone asked similar question before, but the problem asks: The physical ﬁtness of a patient is often measured by the patient’s...

• Replies: 4
• Views: 5,433
10-14-2009, 12:47 PM
31. ### Is a subset of a normal distribution normal?

An easy one for some of you guys here I suspect. Thanks to anyone who can help me with it. I have an application which adds a normally...

• Replies: 4
• Views: 10,342
10-29-2009, 03:54 AM
32. ### law of total expectation (VECTOR case)

" The law of total expectation is: E(Y) = E. It can be generalized to the vector case: E(Y) = E. Further extension: (i) E(Y|X1) = E (ii)...

• Replies: 4
• Views: 5,608
11-21-2009, 12:35 PM
33. ### Probability using z-table

I'm studying for a final and working on some practice problems. I'm stumped on this one and would appreciate any and all help you can provide. The...

• Replies: 4
• Views: 6,101
12-11-2009, 07:42 PM

there is two problems that i can answer .. 1) Processing of the ceramic alloy involves a sintering ( firing ) process which produces a dense hard...

• Replies: 4
• Views: 3,093
01-06-2010, 02:00 PM
35. ### Verify type question

Verify that if X ~ Poisson (mu1) independently of Y ~ Poisson (mu2), then the conditional distribution of X given that X + Y = n is Binomial on n...

• Replies: 4
• Views: 3,012
01-15-2010, 03:16 PM
36. ### Ratio of uniforms is Cauchy

Hi all! I have U is uniform(0,1) and V is uniform(-1,1) such that U^2 + V^2 <= 1. Furthermore, let X=V/U. Show that X is Cauchy. I tried to...

• Replies: 4
• Views: 4,299
02-17-2010, 02:21 PM
37. ### distribution of the range of N independent standard normal variables

Let x1, x2, ... xn be independent standard normal variables. (standard normal: normal with 0 mean and variance 1). Let the range R be defined as...

• Replies: 4
• Views: 7,446
02-20-2010, 01:07 AM
38. ### Joint Density Function Question

So (fy1,fy2) = e^-(y1 + y2) ) , for y1>0, y2>0 and 0 elsewhere. What is P(Y1 + Y2 < 3) The answer is .8009 I just can't work out how to get...

• Replies: 4
• Views: 7,443
02-21-2010, 08:52 AM
39. ### Random Variables and CDF

The problem: A transmission channel is noisy and a binary bit (assume it is a 0 or a 1) has probability of .11 of being incorrectly transmitted. ...

• Replies: 4
• Views: 4,366
02-24-2010, 11:16 AM
40. ### Probability difficulties and Z scores

I am currently grappling with this question: In a certain study the average age was 34.79 years. The SD of age was 14.78. What probability do...

• Replies: 4
• Views: 3,828
02-28-2010, 04:52 PM
41. ### How to calculate the number of samples?

Our company receives wires which are manufactured to our spec in lot sizes that range between 2000 to 20000 wires at a time. These wires should be...

• Replies: 4
• Views: 9,628
03-09-2010, 05:11 AM

Three iid random variables, X, Y and Z with normally distribution with known mean and variances. If two pairs are made, X+Y and Y+Z then are they...

• Replies: 4
• Views: 3,693
BGM
05-08-2010, 03:41 AM
43. ### Machines fail randomly once a month on average.

With one machine how long do I have to wait, on average, for a failure? I don't know when the last failure was. How long for the first failure...

• Replies: 4
• Views: 2,448
03-15-2010, 09:55 AM
44. ### Probability problem

An airline has 500 places for a flight. However, due to only 95% of reservations being taken the airline usually overbooks by 20 places. When the...

• Replies: 4
• Views: 3,126
BGM
03-23-2010, 01:25 PM
45. ### Expected mean question

Suppose that a random variable X has distribution given by P(X = x1) = a = 1 - P(X = x2), where a 2 and x1 != 0 and x2 != 0. (a) Find E i do...

• Replies: 4
• Views: 3,552
BGM
04-15-2010, 06:49 AM
46. ### Normal Distribution

An individuals’ heights are normally distributed with mean 70 and standard deviation 3 (inches). a) What proportion of the population is...

• Replies: 4
• Views: 10,982
04-24-2010, 01:34 AM

thanks much for all ur help!!

• Replies: 4
• Views: 2,664
06-19-2010, 12:55 AM
48. ### How do I add percentages?

For instance, let's say a person is a truck driver and there's an: 80% chance of they smoke 40% chance of they are overweight 60% chance of they...

• Replies: 4
• Views: 7,997
05-03-2010, 11:15 AM
49. ### Simple probability question

Test question: Assume that it is equally likely for a pregnancy to deliver a baby boy or a baby girl. Suppose that for a particular large...

• Replies: 4
• Views: 4,812
05-06-2010, 12:25 PM
50. ### normal approximations

One statistic used to assess professional golfers is driving accuracy, the percent of drives that land in the fairway. Driving accuracy for PGA...

• Replies: 4
• Views: 6,116
06-18-2010, 05:05 PM
51. ### Probability for t=.0419, two independent samples, sample size 10?

Using a student's t-Test, I've found a t-Statistic of .0419 for two independent samples of 10. My problem is getting the corresponding p-Value....

• Replies: 4
• Views: 3,035
06-25-2010, 11:55 AM
52. ### Will rounding off Standard Deviation Bins cause error on Histogram?

I am creating a Histogram. I have about 100 points of data and I am using MS Excel's Histogram function to create the "Bins". The data points I have...

• Replies: 4
• Views: 6,733
06-30-2010, 11:34 AM
53. ### A probability question

52 cards, 13 values (A to K) and 4 suits. what's the probability of getting 5 cards with a four-of-a-kind (same value)? My solution: first card...

• Replies: 4
• Views: 2,675
BGM
06-28-2010, 01:25 PM
54. ### Help

an auther flips a coin 100 times in order to decide whether to use he or she in his book. If it's heads, he uses he. If it's tails, he uses she. What...

• Replies: 4
• Views: 2,597
07-11-2010, 08:53 AM
55. ### Weird Question

Hello all! I have sort of a weird question / request. I'll be taking Mathematical Statistics I and II come Sept and I really want to brush up...

• Replies: 4
• Views: 3,985
07-08-2010, 09:18 PM
56. ### Transformations

Hi! Suppose X ~ U(0,1). If we let Y = -ln (x) and then find the density of Y, we get the exponential distribution (with rate parameter = 1). ...

• Replies: 4
• Views: 4,631
07-12-2010, 03:28 PM
57. ### Discrete Random Variables

Its asking to complete the chart. Since its probability I added it up to have a one but the other chart has a negative does that mean that it can't...

• Replies: 4
• Views: 3,291
07-12-2010, 09:10 PM
58. ### Game Probability

Hi All - I have not looked at statistics or probability for a number of years but am wondering if someone can provide me with a formula for figuring...

• Replies: 4
• Views: 4,080
07-14-2010, 12:26 PM
59. ### technical VS biological replicates (compare means)

Hi, I have conducted an experiment with an assay for 2 biological classes, each consisting of 10 unique members. I did the assay 3 times for a...

• Replies: 4
• Views: 14,060
07-18-2010, 05:49 PM

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