A clear description of how to find the median and quartiles of grouped data.
The median for grouped data can be found either by interpolation or by using a formula.
The formula is
Median =LB+w((1/2 n-∑ f_b)/f_m )
LB is the lower boundary or limit of the class containing the median
w is the width of the median class interval
n is the total frequency, or the number of values
∑ f_b is the number of values below LB
f_m is the number of values containing the median
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