A train 125 m long passes a man, running at 5 km/hr in the same direction in which the train is going, in 10 seconds. The speed of the train is:

(a) 45 km/hr

(b) 50 km/hr

(c) 54 km/hr

(d) 55 km/hr

Explanation:

Speed of the train relative to man = (125/10) m/sec
= (25/2) m/sec.

=(25/2 x 18/5) km/hr

= 45 km/hr.

Let the speed of the train be x km/hr. Then, relative speed = (x – 5) km/hr.
x – 5 = 45

x = 45+5

x = 50 km/hr.