# probability

1. ### Change variable PDF with less variables than before

My question is very simple, I have a probability density function that depends on four variables p(x1,x2,x3,x4). Now each of those variables depend on three new variables, i.e xi=xi(y1,y2,y3) so I want to find the new PDF given by p(y1,y2,y3). The problem is that the jacobian of this...
2. ### Conditional probability

Hello, I'm having an issue with a problem. I just have no clue how to solve it. A machine part may be selected from any of three manufacturers with probabilities p1 = 0.25, p2 = 0.50, and p3 = 0.25. The probabilities that it will function properly during a specified period of time are 0.2...
3. ### Temporal synchronicities

Hi, My cat died five days ago. The day after, when we buried him, I happened to look at my mobile phone at 17.17, 19.19, 21.21. On Tuesday I looked at it at 10.10, 14.14, 15.10, 16.10, 17.17, 20.20, 21.21, 22.22, and yesterday I looked at it at 11.11. I have looked at my phone a few more...
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### binomial distribution problem, calculating probability from a B(p,q) distribution

Hello everyone, I have been trying to solve this Beta distribution problem for quite some time without success. I can get as far as getting the 20 value, but I just cannot tell how the f(x)dx = .3672 is obtained. Underneath is a short description of the problem and on attachment the approach...
5. ### Generating peer nomination dataset in R

Hi all, I have been trying to generate a dataset on peer nominations in R. Often in research participants are asked to nominate others in the peer group (or classroom) as a friend. My requirements Each peer has to nominate x other peers as friends Participants can't select themselves...
6. ### Quick Population / Media Prob question

This is hopefully a fairly quick conditional probability question for you guys. Imagine a total population of 22MM people and I am running a media campaign against 2MM of those people. Secondarily, a survey company has access to a random sample of 4MM of the 22MM population. Each week...
7. ### Help with beginner probability problem?

Hi, I saw this probability question today and I don't understand how the answer was derived. It was about independent events. Could someone explain? Here it is: Elton Brand is shooting free throws. Making or missing free throws doesn't change the probability that he will make his next...
8. ### Normal Distribution

Suppose that in an apartment building run by the Probandstat rental company, the inhabitants's weights follow a normal distribution with mean 73.0 kilos and standard deviation 13.65 kilos. A new elevator must be installed. The elevator company rates the safe carrying capacity of the new...
9. ### bayesian statistics

I have a large amount of data, given totals for every hour over a year period for the following columns: # of Jams Jam event time in minutes # of Full occurances Full event time in minutes and Runtime, product flow (counts) I am trying to create a bayesian model using iPython and...
10. ### Powerball Jackpot

Hello, I need help with my homework! I'm not really good at probability but I really want to learn, if its possible to help me with the answer and how to get to the answer will be great! 2. Assume that each week, on average, 50 million lottery tickets are sold. What are the chances in any...
11. ### Shared car usage

Given a pool of C cars available to use by P people, the arrival rate of drivers to borrow cars is r, and the average trip time is t, how often will there be zero cars available for use?
12. ### C.I. for Bin(n,p) using pivots.

Problem: Let $X$ be $Bin(n,p)$ and $\hat p = X/n$, and $$Z=\frac{\hat p - p}{\sqrt{p(1-p)/n}}$$ We see that $Z$ is asymptotically $N(0,1)$. Find a $1-\alpha$ confidence interval for $p$. Note that this is very different from the regular $$\frac{\hat p - p}{\sqrt{\hat p(1-\hat p)/n}}$$...
13. ### Need help with probability question

So here's my problem: a typical physician performs 4,000 procedures/services per year. These are made up of 75 unique procedures/services. If I were to select 30 line items (each being a reported service or procedure), what is the probability that each of the 30 in the sample would represent...
14. ### Normal Distribution, probability of a certain value

Hi, does anyone know how to do this question? I am really struggling... I know how to find the probability of someone coming within 8 minutes of the advertised time etc, but I don't know how to find the probability of someone arriving at one specific time...? Thanks !:confused::confused...
15. ### Calculating the Probability of a Subset

I'm a newbie and not a stats savvy so help and guidance is appreciated. If I use incorrect terms please forgive and correct. The data set population is 6530 contests, of which 3791 wins, 2731 loses and 8 ties. Probability is .5812 (Note: Ties reduce the number of contests for purposes...
16. ### Two events meeting

Hello everyone, I have a question regarding two events that take place randomly over a certain time period and meet. A similar problem would be phrased as follows, which is maybe simpler: Person A and person B each have 20 balls labelled 1 to 20. Person A picks n number of balls and person...
17. ### stuck with this problem!!!! need help

The minimum force required to break a particular type of cable is normally distributed with mean 12,432 and standard deviation 25. A random sample of 400 cables of this type is selected. Calculate the probability that at least 349 of the selected cables will not break under a force of 12,400...
18. ### Help Settle and Argument re: Chance of Failure in Fantasy Football

Hi, all! I'm new, so please accept my apologies in advance for... whatever. So here's the question. In a fantasy football league, there are two divisions, each with 6 players. In the entire league, there are 3 brothers (each other's brothers!). 2 of the brothers are in division A...
19. ### Probability of goals in a football match?

I am trying to work out the probability of teams scoring a goal in a football match. Obviously there are many factors to consider, and the probability is impossible to predict correctly as there are many factors that will change in a football match. However i want to figure out the probability...
20. ### Determine sample size to get a statistically significant result

Hello, this question concerns the topic of A/B split-testing. More about it on wiki here. I need to determine what is sample size would I require to get a statistically significant result for my experiment. I can see how an economist at Google is doing it. However, our don't understand the...