The following table gives the distribution of the life time of 400 neon lamps. Find the median life time of a lamp.

Solution :

First, we prepare the following table to compute the median :

We have : n = 400 So, $$n\over 2$$ = 200

The cumulative frequency just greater than $$n\over 2$$ is 216 and the corresponding class is (3000 – 3500). Thus, it is the median class.

Here, l = 3000, cf = 130, f = 86 and h = 500.

Substituting these values in the formula,

Median = l + ($${n\over 2} – cf\over f$$)$$\times$$h, we have :

Median = 3000 + $$70\over 86$$ $$\times$$ 500 = 3000 + 406.98 = 3406.98

Hence, median life time is 3406.98 hours.