Aptitude - Problems on Trains - Discussion

B.L. = Bridge Length.

For crossing the bridge distance should be 130+ (B.L) +130.

Then why you are taking 130 + B.L?

Have any common formulas for easily learning?

Here we should consider as per the problem that, Train is passing only one time through the bridge. So 130+B.L. Only sanjay.

I Had one doubt.,

Crossing means we want to consider as opposite direction as formula (u-v) as (375-130) = 245?

Is This Write Or Wrong, If Any One Please Answer Me.

Hai friends don't be confuse with considering different formulas, let use single formula to solve these all type of questions, i.e.

Distance = speed*time; OR (D = ST) ;

Let us consider bridge length = x;

Total length (x+130) = (25/2) *30;

x + 130 = 375;

x = 375-130;

x = 245.

I have solved this problem in another way.

Here am explaining it.

Distance=speed*time;

Length of train = 130m.

Speed = 45 km/hr or 45*1000/3600 m/sec.

Time = 30 sec.

Length = (45*1000/3600)*30 = 375m.

Length of bridge = 375-130 = 245m.

Hi friends, for most of these questions, just understanding the questions is enough and you don't need any formulas.

In the above problem train passes at 45 km/hr so for 1s it will go (45*5/18) = 12.5 m.

And for 30 s it will go 12. 5 * 30 = 375 m.

But we have to reduce trains length (for crossing a pole or person or bridge). So 375-130 = 245 m.

Hi !

Actually we don't know the length of the bridge so we have to assume 'x' as like length of the bridge.

The answer is in meters so we should have to convert 45 km/hr in meters. Because it is in km/hr that's why we are using 5/18.45*5/18 = 25/2.

Train travelling distance and time is 130m+x/30sec = 25/2.

After that we need to find 'x' that is 2 (130+x) = 750. If you solve this equation then you can get 'x' that's the answer.

Why we are multiplying the 60 with 5/18?

The answer is simple. We are converting the 'kilo-meters/hour' value into 'meters/second'.

Let me explain about converting km/hr into m/s in detail.

1 km = 1000 meters.
1 hr = 3600 seconds.

1 km/hr = 1000/3600 m/s

= 10/36 m/s

= 5/18 m/s.

Therefore 1 km/hr = 5/18 m/sec.

Similarly 60 km/hr = 60 x 5/18 m/sec.

You may ask me, why should I convert it from km/hr to m/sec?

Because, the time taken by the train is given in terms of seconds (9 seconds) and the 4 options are in terms of metres. But the speed of the train is given in terms of km/hr. So we have to convert the values from km/hr to m/s in order to find the solution in terms of metres/seconds.

Hope you understand better. Have a nice day guys!

Simplifying the following equation.

45*30*(5/18) = 15*25 = 375 = length of train + length of bridge.

Length of train = 375-130 = 245.