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

Solution:

We prepare the cumulative frequency table, as given below.

We have, $N=400$

So, $\frac{N}{2}=200$

Now, the cumulative frequency just greater than 200 is 216 and the corresponding class is $3000-3500$.

Therefore, $3000-3500$ is the median class.

Here, $I=3000, f=86, F=130$ and $h=500$

We know that

Median $=l+\left\{\frac{\frac{N}{2}-F}{f}\right\} \times h$

$=3000+\left\{\frac{200-130}{86}\right\} \times 500$

$=3000+\frac{70 \times 500}{86}$

$=3000+\frac{35000}{86}$

$=3000+406.98$

$=3406.98$

Hence, the median life of the lamps is approximately 3406.98 hours.