# Questions tagged [probability]

For basic questions about probability and for questions about calculating a probability, expected value, variance, standard deviation, or similar quantity. For questions about the theoretical footing of probability (especially using [tag:measure theory]), ask under [tag:probability-theory] instead. For questions about specific probability distributions, use [tag:probability-distributions] instead.

75,011 questions
Filter by
Sorted by
Tagged with
77 views

### Probability of a disaster

Can you help me with this Markov chain problem? This should be simple, but my brain is not working well. Let $\{{x_t}\}_{t=0}^\infty$ follows a Markov chain. Each $x_t$ can take two values: {G,B} (...
1k views

### Getting exactly $n$ points from coin tossing [duplicate]

Possible Duplicate: A probability question Needing a little help with the following problem, A player tosses a fair coin and is to score one point for every head turned up and two points for ...
356 views

### probability density function of joint density functions

-UPDATED SOLUTION from sasha's hint- Thanks for checking my solution and see if i made any conceptual error. the question http://dl.dropbox.com/u/5681270/Screen%20Shot%202011-11-09%20at%201.40.47%...
689 views

### expected value of battery drawing problem

This is the question: In a box, George has $m$ batteries of which $n$ are dead. He tests them randomly and one by one. Every time that a good battery is drawn, he will return it to the box; every ...
1k views

### Expected time of last bus left

I came across the following problem in a probability exercise, and got confused. The problem is the following. Problem: In a bus station, assume the expected time of next bus arriving is a ...
1k views

### Find standard deviation

The assignment is given: In a heat regulated room, we have two temperature limits $T_{\text{min}} = 16$ and $T_{\text{max}} = 24$. If the temperature is between $T_{\text{min}}$ and $T_{\text{max}}$...
60 views

### Prove (if true): $P(A|C) = \sum_{i} P(A|B_i)P(B_i|C)$

I think the statement $P(A|C) = \sum_{i} P(A|B_i)P(B_i|C)$ is true (where the events $B_i$ form a partition of the whole space). Is it, and why? Thanks!
1k views

### Need a pointer on conditional probability of a fair coin toss

A fair coin is thrown $n$ times. Show that the conditional probability of a head on any specified trial, given a total of $k$ heads over the $n$ trials, is $\frac{k}{n}$ ($k > 0$). I immediately ...
163 views

### Restricted random walk in $\mathbb Z^3$

What is the proability to return to the origin, for a uniform random walk on the integer lattice in $\mathbb Z^3$, if we are restricted to $x \geq 0$? I.e. if we try to step into a negative x-...