If the data set contains an odd number of items, the middle item of the array is the median. If there is an even number of items, the median is the average of the two items. If the total of the frequencies is odd, say n, the value of the (n+1)/2^th  item gives the median and when the total of the frequencies is even, say, 2n, then n^th and (n + 1)^th are two central items and the arithmetic mean of these two items gives the median. 

Example 

The following data relates to the sales figures of certain companies relating to the year 2000-2001:

The median for the above data can be obtained as follows:

The series should first be arranged in an appropriate order. In the present case it is in descending order.

Now, median is the mean of the 5th and the 6th items, i.e.  (412 + 312)/2 = 362.

Thus, the median sales value of the ten companies is 362.