An approximate median can be found for data that have been grouped into a frequency distribution. First it is necessary to find the median class. This is the class that contains the median value. That is the n / 2 data value. Then it is assumed that the data values are evenly distributed throughout the median class. The formula is

where n = sum of frequencies
cf = cumulative frequency of class immediately preceding the median class
w = width of median class
f = frequency of median class
Lm = lower boundary of median class
Using this formula, find the median for data in the frequency distribution of Exercise 15.

MD = (w) +