mean,

The mean is just the **average** of the numbers.

It is easy to calculate: **add up** all the numbers, then **divide by how many** numbers there are.

median,

The Median is the **"middle number"** (in a sorted list of numbers).

To find the Median, place the numbers you are given in **value order** and find the **middle number**.

mode,

The mode is simply the number which appears **most often**.

To find the mode, or modal value, first put the numbers **in order**, then count how many of each number.

This makes it easy to see which numbers appear **most often**.

standard deviation,

*Deviation just means how far from the normal*

The Standard Deviation is a measure of how spread out numbers are.

Its symbol is **σ** (the greek letter sigma)

The formula is easy: it is the** square root** of the **Variance.**

variance

The Variance is defined as the average of the **squared** differences from the Mean.

To calculate the variance follow these steps:

- 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.