Given numbers are 9,21,15,13.
After arranging in ascending order, the sequence obtained is as follows:
9, 13, 15, 21.
Since the number of terms are 4, and 4 is an even number,
∴ median= average of n/2 and n/2+1 observations.
(where n is the total number of observations or terms)
∴ median= (13+15)/2
Hope it helps :)