## Quartiles & Median From Frequency Tables

We start with the table below which summarises the daily sales in a newspaper shop over a year for the 360 days the shop was open.

 Sales Number of Days 1 -200 166 201- 400 100 401 - 700 59 701 - 1000 30 1001 -1500 3

To find the lower quartile we use where are the lower and upper bounds of the frequency class in which the lower quartile lies,1-200, is the total number of data points, is the sum of the frequencies of the classes BELOW that class in which the lower quartile is found and is the frequency of the interval in which the lower quartile is found.

To find the median we use where are the lower and upper bounds of the frequency class in which the median lies, 201-300, is the total number of data points, is the sum of the frequencies of the classes ABOVE that class in which the median is found (in the table above) and is the frequency of the interval in which the median is found.

To find the upper quartile we use where are the lower and upper bounds of the frequency class in which the upper quartile lies, 401-700, is the total number of data points, is the sum of the frequencies of the classes BELOW that class in which the upper quartile is found and is the frequency of the interval in which the upper quartile is found. 