Averages (for a list of numbers)

There are three kinds of average you need to know about for now: the MEAN, the MEDIAN and the MODE. They aren't the only ones, but they're the important ones for GCSE.

Let's say you have a list of numbers: 20, 19, 18, 18, 17, 13, 11, 10 and 8.

The MODE is the MOST COMMON number - here, it's 18. You can remember it by making an elaborate MO! sound, but be careful not to sound like a cow. If you do French, you can remember that la mode means 'fashion' - the mode is the most fashionable number in the list.

The MEDIAN is the MIDDLE number. It's 17 for this list - you get there by counting in from both ends until you reach the middle. Sometimes you get two middle numbers (when the length of the list is even). If the middle numbers are the same, that's your median; otherwise, the median is the number halfway between them (so, if you had 17 and 13 as your middle numbers, the median would be 15). You can remember that median sounds like medium, which means middling; or, if you speak American, you'll know that the middle of a highway (what we call the central reservation) is called the median strip because it's in the middle.

The MEAN is the nasty one. It's the meanest thing they can ask, hence the name. What you have to do is add all of the numbers up and divide by how many there are. The numbers here add to 116, which we have to divide by 9 to get 14.