The median is simply the middle number in a set. However, in order to find the median we must first put the numbers in order from smallest to largest, like this:

15, 16, 17, 18, 18, 18, 19, 19, 20, 20

Note that the numbers which appear more than once are simply listed multiple times.

This list has 10 entries. Since 10 is an even number, there is no single middle number. The middle numbers are both 18.

15, 16, 17, 18, **18, 18,** 19, 19, 20, 20

To find the median we then take the mean of the two middle numbers, which in this case:

`median = (18+18)/2 = 18`

In cases where the set contains an odd number of entries, there is no need to find the mean of two numbers because there is an actual single middle number.

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