## What is the variance of a random variable?

A measure of spread for a distribution of a random variable that determines the degree to which the values of a random variable differ from the expected value. The variance of random variable X is often written as Var(X) or σ2 or σ2x.

**What is PMF and PDF?**

Probability mass functions (pmf) are used to describe discrete probability distributions. While probability density functions (pdf) are used to describe continuous probability distributions.

**Is mean and expected value the same?**

There’s no difference. They are two names for the same thing. They tend to be used in different contexts, though. You talk about the expected value of a random variable and the mean of a sample, population or probability distribution.

### How do you calculate PMF?

The PMF is defined as PX(k)=P(X=k) for k=0,1,2.

**What does a cost variance of 0 mean?**

If the calculated cost variance is zero (or very close to zero), you are on budget. In earned value management, value always comes down to money, whether the commodity is time or actual dollars spent.

**What is PMF PDF and CDF?**

Random Variable and its types. PDF (probability density function) PMF (Probability Mass function) CDF (Cumulative distribution function)

#### How do you do variance?

Variance

- Work out the Mean (the simple average of the numbers)
- Then for each number: subtract the Mean and square the result (the squared difference).
- Then work out the average of those squared differences. (Why Square?)

**What is the sum of the probability of a random variable?**

The probability of each value of a discrete random variable is between 0 and 1, and the sum of all the probabilities is equal to 1. A continuous random variable takes on all the values in some interval of numbers.

**What makes a valid PMF?**

In probability and statistics, a probability mass function (PMF) is a function that gives the probability that a discrete random variable is exactly equal to some value. A PDF must be integrated over an interval to yield a probability.

## What is the square of a random variable?

The square of a random variable is also a random variable. It has all the same properties that you’d expect random variables to have. It has a cumulative distribution function . If it is discrete, then it has a probability (mass) function.

**How do you find the values of a random variables?**

Step 1: List all simple events in sample space. Step 2: Find probability for each simple event. Step 3: List possible values for random variable X and identify the value for each simple event. Step 4: Find all simple events for which X = k, for each possible value k.

**What is the formula for cost variance?**

Cost Variance can be calculated as using the following formulas: Cost Variance (CV) = Earned Value (EV) – Actual Cost (AC) Cost Variance (CV) = BCWP – ACWP.

### Can PMF be negative?

Yes, they can be negative Consider the following game. If we let X denote the (possibly negative) winnings of the player, what is the probability mass function of X? (X can take any of the values -3;-2;-1; 0; 1; 2; 3.)

**How do you find the PMF of a distribution function?**

Note that the CDF completely describes the distribution of a discrete random variable. In particular, we can find the PMF values by looking at the values of the jumps in the CDF function….Suppose the PMF of X is given by PX(k)=12k for k=1,2,3,…

- Find and plot the CDF of X, FX(x).
- Find P(2
- Find P(X>4).

**What is expected value in probability?**

The expected value (EV) is an anticipated value for an investment at some point in the future. In statistics and probability analysis, the expected value is calculated by multiplying each of the possible outcomes by the likelihood each outcome will occur and then summing all of those values.

#### Is S 2 a random variable?

is a normal random variable with mean μ and variance σ 2 / n ; ( n − 1 ) S 2 / σ 2 is a chi-squared random variable with degrees of freedom.

**What is expected value of a random variable?**

The expected value of a random variable is denoted by E[X]. The expected value can be thought of as the “average” value attained by the random variable; in fact, the expected value of a random variable is also called its mean, in which case we use the notation µX. (µ is the Greek letter mu.) xP(X = x).

**What exactly is variance?**

The variance is a measure of variability. It is calculated by taking the average of squared deviations from the mean. Variance tells you the degree of spread in your data set. The more spread the data, the larger the variance is in relation to the mean.

## How do you calculate a PDF?

=dFX(x)dx=F′X(x),if FX(x) is differentiable at x. is called the probability density function (PDF) of X. Note that the CDF is not differentiable at points a and b.

**How do you calculate SV and CV?**

The planned completion should have been 15 percent. Conclusion: Cost Variance (CV) is negative which means the project is over budget and Schedule Variance (SV) is negative that means the project is behind the schedule….Difference between Cost Variance and Schedule Variance:

Cost Variance | Schedule Variance |
---|---|

CV = EV – AC | SV = EV – PV |

**What is CDF in probability?**

Cumulative Distribution Function. The cumulative distribution function (cdf) is the probability that the variable takes a value less than or equal to x. That is. F(x) = Pr[X \le x] = \alpha. For a continuous distribution, this can be expressed mathematically as.

### What is expected value in math?

In probability theory, an expected value is the theoretical mean value of a numerical experiment over many repetitions of the experiment. Expected value is a measure of central tendency; a value for which the results will tend to.

**What is the square of a normal distribution?**

Because the square of a standard normal distribution is the chi-square distribution with one degree of freedom, the probability of a result such as 1 heads in 10 trials can be approximated either by using the normal distribution directly, or the chi-square distribution for the normalised, squared difference between …

**Why expected value is mean?**

The expectation is the average value or mean of a random variable not a probability distribution. As such it is for discrete random variables the weighted average of the values the random variable takes on where the weighting is according to the relative frequency of occurrence of those individual values.