The following table gives the distribution of the life time of 400 neon lamps:
Find the median life time of a lamp.
Cumulative frequency greater than is 216.
So, median class
where, l = lower limit of median class = 3000
n = number of observations = 400
cf = cumulative frequency of class preceding the median class = 130
f = frequency of median class = 86
h = class size (assuming class size to be equal) = 500