For many people, the hardest part of working with measures of central tendency is remembering which average is the mean, the mode or the median. While you could certainly use a straightforward drill until you've memorized them, using mnemonics is simpler and faster for many students.
The mean of a data set is the arithmetic average or the number you get when you add all the values and divide by the number of values in the set. For example, if the set contains 20, 30 and 70, you add them to get 120, and then divide the sum by three to get a mean of 40. Remember that this average is the "mean and nasty" one, because it requires extra calculation, as you first add and then divide.
Thinking about the center median on a highway can help you remember that the median measure is the number that falls exactly in the middle when you place the set values in numerical order. For example, for a set containing 12, 6, 18, 29 and 42, you would begin by putting them in order: 6, 12, 18, 29, 42, which shows that the middle, or median, is 18. Another mnemonic for median is that it starts with the same three letters as "medium," which is the middle size. If you have an even number of values, the median is the mean of the two in the middle. For the data set of 5, 15, 25 and 58, the median is (15+25), divided by 2, which equals 20.
The mode is the number that appears in the set most often. For example, in the set containing 4, 2, 6, 4, 9, 2 and 4, the mode is 4, because it occurs three times, which is more than any other number. If no numbers repeat, there is no mode, which is not the same as having a mode that equals zero. You can remember this by recalling that "mode" and "most" begin with the same two letters.
If poetry speaks to your soul, you can use this verse, from Revision World, to remember all of the measures of central tendency: "Hey, diddle diddle, the median's the middle,/You add then divide for the mean./The mode is the one that you see the most,/And the range is the difference between."
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