Aptitude - Problems on Trains - Discussion

Instead of multiplying 15*20.

We can directly do it by method.

Firstly converting speed = 54*5/18 = 15 m.

Then as we know speed = distance/time.

Since distance = speed *time = 15(36-20) = 15*16 = 240m.

Sorry friends the question was asked about the total length of platform.
So the total length is,

Speed = 54*(5/18) m/sec.
Length between man and starting point of platform = ( 15*20 ) = 300 m.

x be the length between man and end point of platform and train cross the total length in 36 sec.

So,
300 + x is the total length of platform.

( 300 + x )/36 = 15.
= 240.

Total length = 300 + 240 = 540.

Speed = 54*(5/18) m/sec. = 15 m/sec.
length between man and starting point of platform = (15*20) = 300 m.

x be the length between man and end point of platform and train cross the total length in 36 sec.
So,
300 + x is the total length of platform.

(300 + x)/36 = 540.

Ans = 240 m.

Speed = (54 x 5/18) m/sec = 15 m/sec.
Length of the train = (15 x 20)m = 300 m.

Let the length of the platform be x metres.
Then x+300 = 36*15.

(Because: Time taken by a train of length l metres.
To pass a stationary object of length b metres.
Is the time taken by the train to cover (l + b)metres.)

Then x + 300 = 540.
x = 240 m.

Another easy method to solve this problem without using the variable x. Because if we use variable x for all the problems it will b bit confusing.

Solution is in question they asked about length so the formula is.

Distance = speed * time.

Since in question they had given speed in km/hr and the remaining terms are given in seconds added to that answer too given in meters.

Henceforth, its converted to m/sec.

So for converting it is been multiplied with 5/18.
Speed = 54 * (5/18).
= 15.

Since the train and the man in same direction it should be subtracted according to the rule.

So, time = (36-20).
= 16.

Now apply it in the formula.

Distance = speed * time.
= 15 * 16.
= 240.

Answer is 240.

We know that,
s = d*t.

The train has a speed of 54 km/hr.

i.e 54(5/18) = 15 m/sec.
Total distance is sum of train dist and platform distance.

Here we should consider one thing i.e a man is standing 20 sec in plat form during the train crosses the platform. Hence that will gives the length of train So the train length is,
15*20=300 m(s=d*t).

Total distance 300+x ;x is the dist of platform.

Total time 36 sec. So,
300+x/36 = 15.
Finally x = 240 meters.

If the person is standing at the starting point of the platform means the platform length is 240m otherwise its length cannot be calculated. Because if the person standing between any point of platform means it will addition of part of platform and length of train.

If the train cross the platform in 36 sec. Ok in the same time it also cross it's own length of 300 mt. Then we have to subtract the time taken by the train passing it's own length i.e. 20sec.

Then the platform length should be crossed in (36-20) sec =16 sec. Then why (36+20) sec?

Then what is the position of the man on the platform?

I solved in my own knowledge.

./...................

(think "....." it is a platform and a man"/" standing at the very beginning of the platform).

The train passes the station platform in 36 sec and passes the man"/" standing on the platform in 20 sec.

The length of the platform including the man is= 36*15=540 m.
And the length of the man including platform is=20*15=300 m.

So, the length of exact platform=540-300=240 m.