The following table gives the distribution of the life time of 400 neon lamps: \begin{array}{|c|c|} \hline \text{Life time (in hours)} & \text{Number of lamps} \\ \hline 1500 - 2000 & 14 \\ \hline 2000 - 2500 & 56 \\ \hline 2500 - 3000 & 60 \\ \hline 3000 - 3500 & 86 \\ \hline 3500 - 4000 & 74 \\ \hline 4000 - 4500 & 62 \\ \hline 4500 - 5000 & 48 \\ \hline \end{array} Find the median life time of a lamp.