# How do you find the variance of two random variables?

## How do you find the variance of two random variables?

One of the applications of covariance is finding the variance of a sum of several random variables. In particular, if Z=X+Y, then Var(Z)=Cov(Z,Z)=Cov(X+Y,X+Y)=Cov(X,X)+Cov(X,Y)+Cov(Y,X)+Cov(Y,Y)=Var(X)+Var(Y)+2Cov(X,Y).

## When can you add the variances of two random variables?

Even when we subtract two random variables, we still add their variances; subtracting two variables increases the overall variability in the outcomes.

**What is the mean and variance of a random variable?**

We have seen that the mean of a random variable X is a measure of the central location of the distribution of X. The difference here is that we are referring to properties of the distribution of a random variable. The variance of a random variable X is defined by. var(X)=E[(X−μ)2],where μ=E(X).

**What is the variance of the difference between two independent variables?**

For independent random variables X and Y, the variance of their sum or difference is the sum of their variances: Variances are added for both the sum and difference of two independent random variables because the variation in each variable contributes to the variation in each case.

### How to calculate the variance of a random variable?

This is equivalent to multiplying the original value of the variance by 4, the square of the multiplying constant. For independent random variables X and Y, the variance of their sum or difference is the sum of their variances:

### How to find the probability function of a random variable?

Schaum’s Outline of Probability and Statistics CHAPTER 2 Random Variables and Probability Distributions35 EXAMPLE 2.2 Find the probability function corresponding to the random variable Xof Example 2.1. Assuming that the coin is fair, we have Then The probability function is thus given by Table 2-2. P(X0)P(TT) 1 4 P(X1)P(HT

**What is the standard deviation of a random variable?**

= 3.888 + 1.024 + 3.872 + 7.056 = 15.84, with standard deviation = 3.980. This is equivalent to multiplying the original value of the variance by 4, the square of the multiplying constant. For independent random variables Xand Y, the variance of their sum or difference is the sum of their variances:

**How to calculate the sum of two random correlated variables?**

Var(X) is the covariance matrix. If a = (1, 1, …, 1)T, then aTX is the sum of all the x ′ is. Let’s work this out from the definitions. Let’s say we have 2 random variables x and y with means μx and μy. Then variances of x and y would be: Covariance of x and y is: Now, let us consider the weighted sum p of x and y: