Primary Mathematics/Average, median, and mode

From Wikibooks, open books for an open world
< Primary Mathematics
Jump to: navigation, search
Primary Mathematics
 ← Scientific and engineering rotation Average, median, and mode Probability → 

Average, median, and mode[edit]

There are three primary measures of central tendency, and a couple less often used measures, which each, in their own way, tell us what a typical value is for a set of data. Generally, when finding the measures of central tendency, one would order the values of the data set from least to greatest.

===Mode=== Only a true genius can read this without messing up. EYE YAM STEW PID.


is when you do math the right way



Shut up u absoulute twat no one loves you!

Weighted average[edit]

The weighted average or weighted mean, is similar to the straight average, with one exception. When totaling the individual values, each is multiplied by a weighting factor, and the total is then divided by the sum of all the weighting factors. These weighting factors allow us to count some values as "more important" in finding the final value than others.


Let's say we had two school classes, one with 20 students, and one with 30 students. The grades in each class on a particular test were:

Morning class = 62, 67, 71, 74, 76, 77, 78, 79, 79, 80, 80, 81, 81, 82, 83, 84, 86, 89, 93, 98
Afternoon class = 81, 82, 83, 84, 85, 86, 87, 87, 88, 88, 89, 89, 89, 90, 90, 90, 90, 91, 91, 91, 92, 92, 93, 93, 94, 95, 96, 97, 98, 99

The straight average for the morning class is 80% and the straight average of the afternoon class is 90%. If we were to find a straight average of 80% and 90%, we would get 85% for the mean of the two class averages. However, this is not the average of all the students' grades. To find that, you would need to total all the grades and divide by the total number of students:

Or, you could find the weighted average of the two class means already calculated, using the number of students in each class as the weighting factor:

Note that if we no longer had the individual students' grades, but only had the class averages and the number of students in each class, we could still find the mean of all the students grades, in this way, by finding the weighted mean of the two class averages.

Geometric mean[edit]

The geometric mean is a number midway between two values by multiplication, rather than by addition or subtraction. For example, the geometric mean of 3 and 12 is 6, because you multiply 3 by the same value (2, in this case) to get 6 as you must multiply by 6 to get 12. The mathematical formula for finding the geometric mean of two values is:


A = one value
B = the other value

So, in our case:

Note the new notation used to show multiplication. We now can omit the multiplication sign and show simply AB to mean A×B. However, when using numbers, 312 would be confusing, so we put parenthesis around at least one of the numbers to make it clear.

The geometric mean can be extended to additional values:

For three values, a cube root is performed instead of a square root. On four values, the fourth root is performed.

Primary Mathematics
 ← Scientific and engineering notation Average, median, and mode Probability →