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### Discussion :: Problems on Trains

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:

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

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.

 $$[\frac { 100+100 } {8 } ]$$ = 3x

24x = 200

 x = $$\frac { 25 } { 3 }$$ .
 So, speed of the faster train = $$\frac {50 } { 3}$$ m/sec
 = [$$\frac {50 } { 3}$$ x $$\frac { 18 } { 5} ]$$ km/hr

= 60 km/hr.

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