The following table gives the distribution of the life time of 400 neon lamps :

Life time (in hours)	Number of lamps
1500 - 2000	14
2000 - 2500	56
2500 - 3000	60
3000 - 3500	86
3500 - 4000	74
4000 - 4500	62
4500 - 5000	48

Find the median life time of a lamp.

Cumulative frequency distribution table is as follows :

Here, n = 400, $\dfrac{n}{2} = \dfrac{400}{2} = 200$.

Cumulative frequency just greater than 200 is 216, belonging to class-interval 3000 - 3500

∴ Median class = 3000 - 3500

⇒ Class size (h) = 500

⇒ Lower limit of median class (l) = 3000

⇒ Frequency of median class (f) = 86

⇒ Cumulative frequency of class preceding median class (cf) = 130

By formula,

Median = $l + \Big(\dfrac{\dfrac{n}{2} - cf}{f}\Big) \times h$

Substituting values we get :

$\Rightarrow \text{Median } = 3000 + \dfrac{200 - 130}{86} \times 500 \\[1em] = 3000 + \dfrac{35000}{86} \\[1em] = 3000 + 406.98 \\[1em] = 3406.98$

Hence, median life = 3406.98 hours.