Type To 1 5 X 4

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• X 1 X 4 X 3 0
• Type To 1 5 X 4 5 Picture Frame

A Random Variable is a set of possible values from a random experiment.

Example: Tossing a coin: we could get Heads or Tails.

1 4 2 X 1 10 X

Let's give them the values Heads=0 and Tails=1 and we have a Random Variable 'X':

In short:

X = {0, 1}

Note: We could choose Heads=100 and Tails=150 or other values if we want! It is our choice.

So:

• We have an experiment (such as tossing a coin)
• We give values to each event
• The set of values is a Random Variable

Not Like an Algebra Variable

In Algebra a variable, like x, is an unknown value:

Example: x + 2 = 6

In this case we can find that x=4

But a Random Variable is different ..

Example: X = {0, 1, 2, 3}

X could be 0, 1, 2, or 3 randomly.

And they might each have a different probability.

Capital Letters

We use a capital letter, like X or Y, to avoid confusion with the Algebra type of variable.

Sample Space

A Random Variable's set of values is the Sample Space.

Example: Throw a die once

Random Variable X = 'The score shown on the top face'.

X could be 1, 2, 3, 4, 5 or 6

So the Sample Space is {1, 2, 3, 4, 5, 6}

Probability

We can show the probability of any one value using this style:

P(X = value) = probability of that value

Example (continued): Throw a die once

X = {1, 2, 3, 4, 5, 6} Cyberduck 6 4 6 – ftp and sftp browser free.

Iflicks 2 4 3 download free. In this case they are all equally likely, so the probability of any one is 1/6

• P(X = 1) = 1/6
• P(X = 2) = 1/6
• P(X = 3) = 1/6
• P(X = 4) = 1/6
• P(X = 5) = 1/6
• P(X = 6) = 1/6

Note that the sum of the probabilities = 1, as it should be.

Example: How many heads when we toss 3 coins?

X = 'The number of Heads' is the Random Variable.

In this case, there could be 0 Heads (if all the coins land Tails up), 1 Head, 2 Heads or 3 Heads.

So the Sample Space = {0, 1, 2, 3} Charles 4 2 5 – java http proxy and monitor.

But this time the outcomes are NOT all equally likely.

The three coins can land in eight possible ways:

Looking at the table we see just 1 case of Three Heads, but 3 cases of Two Heads, 3 cases of One Head, and 1 case of Zero Heads. So:

• P(X = 3) = 1/8
• P(X = 2) = 3/8
• P(X = 1) = 3/8
• P(X = 0) = 1/8

Example: Two dice are tossed.

The Random Variable is X = 'The sum of the scores on the two dice'.

Let's make a table of all possible values:

So:

• We have an experiment (such as tossing a coin)
• We give values to each event
• The set of values is a Random Variable

Not Like an Algebra Variable

In Algebra a variable, like x, is an unknown value:

Example: x + 2 = 6

In this case we can find that x=4

But a Random Variable is different ..

Example: X = {0, 1, 2, 3}

X could be 0, 1, 2, or 3 randomly.

And they might each have a different probability.

Capital Letters

We use a capital letter, like X or Y, to avoid confusion with the Algebra type of variable.

Sample Space

A Random Variable's set of values is the Sample Space.

Example: Throw a die once

Random Variable X = 'The score shown on the top face'.

X could be 1, 2, 3, 4, 5 or 6

So the Sample Space is {1, 2, 3, 4, 5, 6}

Probability

We can show the probability of any one value using this style:

P(X = value) = probability of that value

Example (continued): Throw a die once

X = {1, 2, 3, 4, 5, 6} Cyberduck 6 4 6 – ftp and sftp browser free.

Iflicks 2 4 3 download free. In this case they are all equally likely, so the probability of any one is 1/6

• P(X = 1) = 1/6
• P(X = 2) = 1/6
• P(X = 3) = 1/6
• P(X = 4) = 1/6
• P(X = 5) = 1/6
• P(X = 6) = 1/6

Note that the sum of the probabilities = 1, as it should be.

Example: How many heads when we toss 3 coins?

X = 'The number of Heads' is the Random Variable.

In this case, there could be 0 Heads (if all the coins land Tails up), 1 Head, 2 Heads or 3 Heads.

So the Sample Space = {0, 1, 2, 3} Charles 4 2 5 – java http proxy and monitor.

But this time the outcomes are NOT all equally likely.

The three coins can land in eight possible ways:

Looking at the table we see just 1 case of Three Heads, but 3 cases of Two Heads, 3 cases of One Head, and 1 case of Zero Heads. So:

• P(X = 3) = 1/8
• P(X = 2) = 3/8
• P(X = 1) = 3/8
• P(X = 0) = 1/8

Example: Two dice are tossed.

The Random Variable is X = 'The sum of the scores on the two dice'.

Let's make a table of all possible values:

There are 6 × 6 = 36 possible outcomes, and the Sample Space (which is the sum of the scores on the two dice) is {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12}

Let's count how often each value occurs, and work out the probabilities:

• 2 occurs just once, so P(X = 2) = 1/36
• 3 occurs twice, so P(X = 3) = 2/36 = 1/18
• 4 occurs three times, so P(X = 4) = 3/36 = 1/12
• 5 occurs four times, so P(X = 5) = 4/36 = 1/9
• 6 occurs five times, so P(X = 6) = 5/36
• 7 occurs six times, so P(X = 7) = 6/36 = 1/6
• 8 occurs five times, so P(X = 8) = 5/36
• 9 occurs four times, so P(X = 9) = 4/36 = 1/9
• 10 occurs three times, so P(X = 10) = 3/36 = 1/12
• 11 occurs twice, so P(X = 11) = 2/36 = 1/18
• 12 occurs just once, so P(X = 12) = 1/36

A Range of Values

We could also calculate the probability that a Random Variable takes on a range of values.

Example (continued) What is the probability that the sum of the scores is 5, 6, 7 or 8?

In other words: What is P(5 ≤ X ≤ 8)?

Solving

We can also solve a Random Variable equation.

Example (continued) If P(X=x) = 1/12, what is the value of x?

Looking through the list above we find:

• P(X=4) = 1/12, and
• P(X=10) = 1/12

So there are two solutions: x = 4 or x = 10

Notice the different uses of X and x:

• X is the Random Variable 'The sum of the scores on the two dice'.
• x is a value that X can take.

Continuous

Random Variables can be either Discrete or Continuous:

• Discrete Data can only take certain values (such as 1,2,3,4,5)
• Continuous Data can take any value within a range (such as a person's height)

All our examples have been Discrete.

Learn more at Continuous Random Variables.

Mean, Variance, Standard Deviation

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You can also learn how to find the Mean, Variance and Standard Deviation of Random Variables.

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Summary

• A Random Variable is a set of possible values from a random experiment.
• The set of possible values is called the Sample Space.
• A Random Variable is given a capital letter, such as X or Z.
• Random Variables can be discrete or continuous.