Aptitude - Problems on Trains - Discussion

I am done my way.
If its takes 24s to cross 240m,
So how much it'l take to cross 650m long platform. 240+650=890.
You just put one equation like.
240m=24s.
890m=?, then cross multiplication.
890*24/240=89.

Train of length 240 mts.....
It covers 240 mts in 24 sec...
During crossing a bridge it has to cover 650 mts additional to 240....
So 240mts in 24 sec
Then (240+650) in x sec
i.e x=24*890/240===>89

Total distance= Total length of train + Length of platform

@sonal,
First we find the TIME of the train. So we get 240/24=10m/1s.
Next we find the total DISTANCE of the train. So we get 240+650=890.
Finally.
Speed=distance/time.
=890/10.
=89sec.

Thanku Rahul for clearing Confusion :)

Thanks Kirubanidhi for the right explanation :).

Can you tell me, why did we get 240 two times?

(Firstly 240/24, then after 240+650/10) So please explain me.

If we are asked only the time taken to cover 650 m long platform, then the rigth answer is 65.

If we are asked to find the total time to cover the whole distance (240+650) , then the rigth answer is 89.

Guys.. i can suggest u one thng that don't depend entirely on formulas, try

to analyze these type of problems logically..

coming to the prblm..

length of train = 240 mts

time taken to cross reference point(pole) = 24 sec

by the basic formula speed=length/time= (240/24) = 10 m/sec

they are asking the time taken by the train to cross the platform

imagine

------------------------- its a platform
650 m
______________ its train
240 m

train is said to be crossed the platform only if the entire train has pased over from it ryt... so clearly the total length that has to be travel to cross the platform is= (platform length + train length)

i.e. 650+240=890 m/sec

and again from the basic formula time= length/speed = 890/10 = 89 sec

For problems on trains for most of the problems we use one formulae

time=(l1+l2)/s1+s2

for eg in the above problem

given length of train 240m and time 24 sec then speed=10m/sec

given length of platform 650

their is no speed s2 because platform is a stationary object

so substitue all the values in above formulae

we get time t=(240+650)/10= 89sec