# Tagged Questions

This tag is for basic questions about probability and for questions in which one wants to calculate a probability, expected value, variance, standard deviation, or similar quantity. For questions about the theoretical footing of probability (especially using measure theory), please ask under (...

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### Knight (Chess) Problem on telephone keyboard

There is phone keyboard with Knight on 0 (as shown below). 123 456 789 0 Knight moves as per the rules of chess (2 straight and one turn). T is no. of moves ...
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### How to compute variance of a conditional expectation and vice versa

I am trying to use the law of total variance which is $$\operatorname{Var}(X) = \text{Var}(E(X\mid Y)) + E(\operatorname{Var}(X\mid Y))$$ But I honestly have no idea how to compute either one of ...
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### Variance of a discrete random variable with 4 outcomes

Say we have an event with four possible outcomes $(1,2,3,4)$ each with equal probabilities of occurring. A random variable $Y$ is defined as the number of outcome 1's that occur over $n$ events. ...
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### Which of the following is true for random variables $X$ and $Y$?

Suppose $X$ and $Y$ are two random variables such that $aX+bY$ is a normal random variable for all $a,b \in \mathbb{R}$. Consider the following statements P, Q, R and S: (P) : $X$ is a ...
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### Probability and Decision Tree

The task in hand is the following: There are N entities (E1..EN). There are M questions (Q1..QM). Each question has at least two options (can be different number of options of different questions). ...
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### Probability question confusion

A bag consists 20 cards contains 4 cards of each Colours, red , green , blue , yellow and white . The four cards of Each Colour are numbered 1,2,3,4 respectively . One card is selected at random . ...
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### Probability of two statistically independent, uniformly distributed variables occurring within time frame of each other?

Say two events will occur independently of each other, only once each. The time of each event occurring is uniformly distributed from 0 to 10 seconds. What is the probability that the events will ...
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