Question on Speed & Distance

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 by cycle at 10 km/h. The average of the tourist in km/h during his entire journey is

(A) 36
(B) 30
(C) 24
(D) 18

Answer: (C)

Explanation :

Lets assume the distance = X

Time it took for the tourist to cover first part of the journey = (X/2)/60 = X/120
Time it took for the tourist to cover second part of the journey = (X/4)/30 = X/120
Time it took for the tourist to cover third part of the journey = (X/4)/10 = X/40

Total time it took for the journey = X/120 + X/120 + X/40 = 5X/120

Average speed of the journey = Distance/ Time = X / (5X/120) = 120/5 = 24 Kmph