Three little measures, one golden rule: sort the list before you touch it. This lesson nails median (including the even-count case), mode and range — and the mix-ups between them.
Sort the list, cross off from both ends to the centre. 3, 3, 5, 7, 9 → median 5.
The value that appears most often. 3 appears twice → mode 3. (No repeats → no mode.)
9 − 3 = 6. The range measures spread, not an average.
Find the median, mode and range of 12, 8, 12, 15, 8, 12.
Order first! Sorted: 3, 3, 5, 7, 9 → the middle is 5.
Wrong! Mode = MOST COMMON, not largest: 3.
One number! Range = biggest − smallest = 9 − 3 = 6.
The mean shares the total equally (total ÷ count); the median is the middle of the ordered list; the mode is the most common value. They can all be different for the same data.
Take the two middle values of the ordered list and find the number halfway between them: for 2, 4, 6, 10 the median is (4 + 6) ÷ 2 = 5.
Biggest value minus smallest value — it measures how spread out the data is, and it's written as a single number.
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