# A-level Mathematics/MEI/S1/Discrete Random Variables

## Discrete Random Variables[edit]

Discrete random variables are the models for the probabilities of particular results. They are represented by the notation, ** (Where P is the probability of the Discrete Random Variable, X , taking on the result, R.). A discrete random variable can only take on the values ****r _{1},r_{2},r_{3}...r_{n}** with the probabilities

**p**respectively. Discrete random variables allow us to produce a

_{1}, p_{2}, p_{3}...p_{n}**Discrete Frequency Distribution**. Discrete meaning that the value of the results can only take on positive whole integers. In S1, Discrete distributions are limited to a finite number of outcomes.

## Exemplar Question[edit]

Questions often involve working with algebra in order to find the probabilities, in OCR(MEI), you will often have to work out the value of **k** in order to work out the probabilities.

**The probability distribution of a discrete random variable, X, is given by**

```
```

**Find the value of k and tabulate the probability distribution.**

To find the value of k, we need to tabulate our probabilities and substitute the values of R into the discrete random variable, X.

```
R || 2 | 4 | 6 | 8 ||
p(x=R)||
```