Aptitude - Problems on Trains - Discussion

I can't understand step 2 mohanraj can you explain again clearly.

Why we take x/y=15 can you please explain me?

@pavan

Since we have declared x-distance,y-speed
According to the below given formula,

Time=Distance/speed
Here Train speed time is specified as 15 sec so,
15 =x/y

other way is select any option and solve for both case

i think i will try explain simple
1.s=d/t=x(length or distance covered by train)/15
s=x/15
2.the same train to cross cross 100m long platform is
s=d/t
x/15(it's by step1) =(100+x)/25
then we can get x=150m
thank u

sorry for late reply..to pbn..
in train pblms length=distance..
in step 2 the length of thetrain is added with the length of the platform tat it s crossin..X+100(100 is length of the platform)
than asusual.speed=dis/tim=100+x/25
25 is the time aftrcrossing the platform.. it think u got.

Hi,.

Can any one explain me why they have taken 15 sec for calculating speed of train but not 25 sec?

100+L/25=SPEED
L/15=SPEED
(100+SPEED*15)=25*SPEED
100=10SPEED
SPEED=10
LENGTH L= 150.

Nayan correctly said! why they have taken 15 sec for calculating speed of train but not 25 sec? Since distance of signal pole is included in platform, we have to take time taken by train to pass the plateform, and not pole.

You see they took a signal post because it has a single point kk here we can calculate the speed .

Where as in platform we have two points so we have to add the platform length also to calculate the speed .

So guys we can calulate the speed of the train with one point is very easy So they took 15 sec as the refernce for speed of the train. got it?

If you want to calculate with 25 sec as refernce u should slove by option verification .

150+100=250mts
Total time = signalpost+platform length

25 sec = 15 sec +platform length
platform length =10 sec

so , 250mts/25sec=10mts/sec
So ans is 150 mts.

Is our ans is correct or not let us verify
10mts=1 sec
total length length of plat form time is 10 sec so ,
we have 1 sec=10 mts
10 sec=?
100mts so our ans tallied
We got length of the platform.