Mean, median and mode are the three basic ways of looking at the average or typical value of a set of numbers.
The mean represents the pure average, and, in fact, the word “mean” is often interchangeable with the word “average.” To find the mean of a set of numbers you add up all of the numbers and divide that sum by the number of values you added together.
For example, let’s say you want to know your score so far in a course where there have been five equally weighted assignments. So far you’re scores have been 95, 89, 70, 90, and 98.
First add these numbers together.
Now you divide that number, 442, by the number of assignments you’ve had so far, which is 5.
So your score in that class right now is 88.4.
The median number is the number that is in the middle of a set of numbers. To find the median you first need to order the numbers from smallest to largest. So, using the scores from above:
70, 89, 90, 95, 98
Now find the one in the middle. That’s your median. 90 is the median test score.
If you have an even number of values, find the two in the middle and find the mean of those two. For example, let’s say you just got another assignment back. And, congratulations, you got a 100! Just order all the scores as before.
70, 89, 90, 95, 98, 100
Find the two in the middle: 90 and 95. Average them.
Your median is now 92.5.
The mode is the value that occurs the most often in a set of values. To find the mode, count the number of times the most common numbers occur. The one that occurs the most often is the mode. Since the assignment scores are all different numbers there is no mode in the example above. Let’s say instead that for assignment 3 the scores for each student were as follows
90, 84, 59, 78, 97, 91, 90, 84, 96, 89, 80, 79, 91, 99, 86, 91
What is the mode? You will be able to see common occurrences more easily if you order the numbers. If you do that you will see that there are two 84s, two 90s and three 91s. 91 occurs the most often, so 91 is the mode.