Aptitude - Problems on Trains - Discussion

Yes answer is correct but checking through reverse process.

Let x = 82 km/h and we have find time to cross each other. Then then the answer will come 6 sec. So it is correct.

How the final answer comes in km per hour? First we are converting into metre per second so we need to convert it into km per hour.

Distance = (220/1000) km {Want to convert meter into kilometer).

Time = (6/3600) seconds {Second into hours - one hour has 3600 seconds}.

Distance/Time = Speed.

= (220/1000)/(6/3600) = x+50 km {Opposite speed should be added).

Now without converting, follow normally:

220/6*3600 = (50+x) speed (If goes 220 m within 6 seconds, what is the distance per hour or 3600 seconds).

132000 m per hour = (50+x).

So, 132 kilometer = (50+x).

x = 132-50 = 82.

S = D/T.

So, D = 108+112 = 220 m.

= 220/1000 km/hr.

T = 6 sec = 6/3600 = 1/600 hr.

S = 50 km/hr.

We assume second train speed 'x'.

Relative speed = 50 km/hr+x km/hr.

S = D/T.

= 50+x = 220/1000*600.

= 50+x = 22*6 = 50+x = 132.

x = 82 km/hr.

But can't do in direct formula of a + b/u + v = t? Then finding us there.

50*5/18 = 13.889 m/sec.
108 + 112/13.889 + x = 22.778.

Since it has to be in km/hr.
23.778*18/5 = 82 km/hr.

Total distance = 112 + 120 = 220 m.

Time = 6 sec.

Relative speed = total distance / time,

=> 220/6 m/s

Speed in km/h,

=> 220/6 * 18/5 = 132.

Speed of second train = relative speed - speed of 1st train,

=> 132- 50 = 82 km/h.