Aptitude - Problems on Trains - Discussion

Suppose the length of the train is X.
Therefore speed X/15,
As given 25 * X/15 = 100 + X,
25X = 1500 + 15X,
25X - 15X = 1500,
10 X = 1500,
X = 150.

Speed of train = length of platform/difference of time.
= 100/(25 - 15) = 10km/h.

Then distance=speed * time.
= 10 * 15 = 150 m.

Why are you adding the length of the platform and length of the train X+100?

In the question, the distance between pole and platform is nowhere mentioned.

We know, suppose speed = x & length = L.

L/15 = x.

Or L = 15 x.

Now,

(L +100) / 25 = x.

Can we substitute for L here.

(15 x + 100) / 25 = x.

15 x + 100 = 25 x.

100 = 10 x.

X = 10.

L = 15 * 10 = 150.

Simplest way to solve this.

A train speeds past a pole in 15 seconds and a platform 100 m long in 25 seconds.
Its length is:
Train speeds past a pole in 15 (distance/length unknown).
Train speeds past a platform of 100 m in 25 sec. it take 10 sec more to cross 100 m so to find out how much will it travel in 15 seconds is easy.

15 x 100/10 = 150.
Answer is 150 meters

Hope it helps you.

Let,
Length(distance) of the train = x meters.
Here time = 15 sec.

We know, Speed = d/t
=> x/15 m/sec.
Then,
100 + x = x
----------------------------
25 15
25x = 1500 + 15x.
25x - 15x = 1500
10x = 1500
x = 150 meters ==>answer.

Please tell me the answer.

If a train crosses 300 metres long platform in 38 seconds while it crosses a signal pole in 18 seconds. What is the speed of the train in km/h?

Let the length of the train= l meters.

We know speed = length/ time.
So, speed of the train = l/15 m/sec.

To cross the platform the train have to cover = length of the train + length of the platform [ this is the relative distance].

So total length = l+100.

l+100=(l/15)*25 [applying the rule:- length = speed*time.
=> l+100= 25l/15 m.
=> l+100= 5l/3 m.
=> 3l+300= 5l m.
=> 5l-3l= 300 m.
=> 2l=300 m.
=> l= 150 meters.

The length of the train is 150 meters.

Let speed = X; then length of train = 15 X;

Hence (15X+100)/X = 25.

Answer the length of train is 15X = 10*15 = 150.