How do you find the standard deviation of a discrete random variable

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What is the standard deviation of the discrete random variable?
How do you find the standard deviation of a random variable?

We have two independent, normally distributed random variables

and such that has mean and variance and has mean and variance . What is the probability distribution of the difference of the random variables, ?

Possible Answers:

Normal distribution with mean and variance .

Correct answer:

Normal distribution with mean and variance .

Explanation:

The mean for any set of random variables is additive in the sense that

The difference is also additive, so we have

This means the mean of is .

The variance is additive when the random variables are independent, which they are in this case. But it's additive in the sense that for any real numbers (even when negative), we have

So for this difference, we have

So the mean and variance are and , respectively. In addition to that, is normally distributed because the sum or difference of any set of independent normal random variables is also normally distributed.

If and are two independent random variables with and , what is the standard deviation of the sum,

Correct answer:

Explanation:

If the random variables are independent, the variances are additive in the sense that

So then the variance of the sum is

The standard deviation is the square root of the variance, so we have

Consider the discrete random variable that takes the following values with the corresponding probabilities:

Compute the probability .

Correct answer:

Explanation:

This probability is simple to compute:

We want to add the probability that X is greater or equal to two. This means the probability that X=2 or X=3.

Adding the necessary probabilities we arrive at the solution.

Consider the discrete random variable that takes the following values with the corresponding probabilities:

Compute the expected value of the distribution.

Correct answer:

Explanation:

The expected value is computed as

for any values of x that the random variable takes.

So we have

The average number of calories in a Lick Yo' Lips lollipop is , with a standard deviation of . The calories per lollipop are normally distributed, so what percent of lollipops have more than calories?

Correct answer:

Explanation:

The random variable number of calories per lollipop, so the answer is

Robert's work schedule for next week will be released today. Robert will work either 45, 40, 25, or 12 hours. The probabilities for each possibility are listed below:

45 hours: 0.3

40 hours: 0.2

25 hours: 0.4

12 hours: 0.1

What is the standard deviation of the possible outcomes?

Correct answer:

Explanation:

There are four steps to finding the standard deviation of random variables. First, calculate the mean of the random variables. Second, for each value in the group (45, 40, 25, and 12), subtract the mean from each and multiply the result by the probability of that outcome occurring. Third, add the four results together. Fourth, find the square root of the result.

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What is the standard deviation of the discrete random variable?

The standard deviation of X is defined to be the square root of the variance of X. That is, sd(X)=σX=√var(X). Because of this definition, the variance of X is often denoted by σ2X.

How do you find the standard deviation of a random variable?

First, calculate the mean of the random variables. Second, for each value in the group (45, 40, 25, and 12), subtract the mean from each and multiply the result by the probability of that outcome occurring. Third, add the four results together. Fourth, find the square root of the result.