Calculations of Quartiles from Grouped Observations

Quartiles: 

where

            l = lower limit of the quartile class,

            h = width of the quartile class,

            f = frequency of the quartile class

            c= cumulative frequency of the class preceding the quartile class

            n =total frequency

            i = 1, 2, 3

For example, the maximum days first 25% and 75% days to maturity of 40 short-term investments (Table 2) are:  

Table 2: Days to maturity 40 short-term investments.

Class interval	Frequency	Cumulative frequency
30—39	3	3
40—49	1	4
50—59	8	12
60—69	10	22
70—79	7	29
80—89	7	36
90—99	4	40
Total	40