6 The average speed of a bus, \(x \mathrm {~km} \mathrm {~h} ^ { - 1 }\), on a certain journey is a continuous random variable \(X\) with probability density function given by $$f ( x ) = \begin{cases} \frac { k } { x ^ { 2 } } & 20 \leqslant x \leqslant 28
0 & \text { otherwise } \end{cases}$$

1. Show that \(k = 70\).
2. Find \(\mathrm { E } ( X )\).
3. Find \(\mathrm { P } ( X < \mathrm { E } ( X ) )\).
4. Hence determine whether the mean is greater or less than the median.