1.  Two trains, each 100 m long, moving in opposite directions, cross each other in 8 seconds. If one is moving twice as fast the other, then the speed of the faster train is:

A. 30 km/hr
B. 45 km/hr
C. 60 km/hr
D. 75 km/hr

Answer: Option C

Explanation:

Let the speed of the slower train be x m/sec.

Then, speed of the faster train = 2x m/sec.

Relative speed = (x + 2x) m/sec = 3x m/sec.

(100 + 100) = 3x
8

24x = 200

x = 25 .
3

So, speed of the faster train = 50 m/sec
3

   = 50 x 18 km/hr
3 5

   = 60 km/hr.