Aptitude - Problems on Trains - Discussion

Please some one explain me in detail. Thank you

Hi Chanda,

If two trains (or bodies) start at the same time from points A and B towards each other and after crossing they take a and b sec in reaching B and A respectively, then:

(A's speed) : (B's speed) = (b : a)

Please explain me only the last step.

Hi Deepika

The last step is converting m/sec to km/hr.

But i am not understanding how can the dist be equated?
(x - 1.25) x 8.4 = (x - 1.5) x 8.5
can any one explain it plz.

@Gowthami

4.5km/hr=4.5x5m/sec =5m/sec=1.25m/sec
5.4km/hr=5.4x5m/sec=3m/sec=1.5m/sec
then speed of the train=x
distance=speed*time
so distance=(x-1.25)*8.4-------------1
distance=(x-1.5)*8.5----------------2
(1)=(2)
(x - 1.25) x 8.4 = (x - 1.5) x 8.5

There is no need of confusion regarding this problem.
in this problem...train and the two persons are moving in the same direction...

Consider the speed of the train be X km/hr.
**(note:the SPEED and LENGTH remains same in both the cases)****
----------------------------------------------------------------
now let us consider relative speed of the train w.r.to the first person..we get...(X-1.25)
in similar manner,relative speed w.r.to the second train...we get...(X-1.5)
(NOTE:why i'm doing subtraction here ,since they are moving in the same direction)

now we know,distance=speed*time
(x - 1.25) x 8.4 = (x - 1.5) x 8.5
8.4x - 10.5 = 8.5x - 12.75
0.1x = 2.25
x = 22.5
speed of the train=22.5 * (5/18)=81km/hr

Good explanation. Thank you manasa.

But as manasa said why to equal both the relative speed's.

I am not understanding. Can any one please help me.

But the two man is also moving then there is change in distance, so how then (x-1.25)x8.4=(x-1.5)x8.5 both are moving so both the distance are varying.

Can some one please explain this?

How can we assume that the distance is equal ?