The median is the middle value of a data set when the values are listed from least to greatest. Half of the values are at or below the median, and half are at or above the median.

To find the median:

1. Order the values from least to greatest.
2. Cross off from both ends of the list — one from the left, one from the right — until you reach the middle.
3. If there is one middle value (an odd number of values), that value is the median.
4. If there are two middle values (an even number of values), the median is the average of those two values: add them and divide by 2.

Odd N example: The data set 4, 7, 9, 12, 15 has 5 values. The middle (3rd) value is 9, so the median is 9.

Even N example: The data set 6, 10, 14, 18 has 4 values. The two middle values are 10 and 14. The median is (10 + 14) / 2 = 24 / 2 = 12.

Split-the-difference example: The data set 18, 22, 25, 27 has 4 values. The two middle values are 22 and 25. The median is (22 + 25) / 2 = 47 / 2 = 23.5. The median doesn't have to be a whole number, and it doesn't have to be a value that's actually in the data set.