The average speed of the tourist in km/h during his entire journey is

Question

A tourist covers half of his journey by train at 60 Km/h, half of the remainder by bus at 30 km/h and the rest of cycle at 10 km/h. The average speed of the tourist in km/h during his entire journey is                                               

      (a) 36                                                                  (b) 30

      (c) 24                                                                  (d) 18