Simply defined, the median is the number right in the middle of a set.
But before I get down to finding the median, I will order the numbers from least to greatest:
15, 17, 19, 20, 21, 22, 23
Now, the middle number is 20. So that's the median.
As for the range, it's the difference between the largest number and the smallest one:
Range = Greatest number - Smallest number
= 23 - 15
= 6
In summary, the median, the number in the middle, is 20, and the range, the difference between the largest number and the smallest one, is 6.