Aptitude - Problems on Trains - Discussion

I think 65 is the correct answer.

And why we add 240 +650?

240 mtrs -- 24 sec.
890 mtrs-- x sec.

ie..890 * 24/240 = 89 sec.

240÷10 = 24.
650÷10 = 65.
65 + 24 = 89.

We need to find the time that will take to pass a platform of 650 m.

Therefore, Time = Distance/Speed.
Speed is not given so need to find speed with given values.
Speed = Distance / Time.
= 240 m/24 sec.
= 10 m/sec.

Now we have Distance and Speed to calculate Time that will take to pass 650 m platform.
Time = (650 + 240)m/10 m/sec.
= 890/10 sec.
= 89 sec.

Note : If a train passes a tunnel, bridge, platform then distance covered by train is Length of the train + Length of tunnel (or) bridge (or) platform.

That's why we are adding Length of train + Length of the platform in Distance while calculating Time.

Should not consider the only Length of the platform(650 m).

We need to find the time that will take to pass a platform of 650 m.

Therefore, Time = Distance/Speed.
Speed is not given so need to find speed with given values.
Speed = Distance / Time.
= 240 m/24 sec.
= 10 m/sec.

Now we have Distance and Speed to calculate Time that will take to pass 650 m platform.
Time = (650 + 240)m/10 m/sec.
= 890/10 sec.
= 89 sec.

Note : If a train passes a tunnel, bridge, platform then distance covered by train is Length of the train + Length of tunnel (or) bridge (or) platform.

That's why we are adding Length of train + Length of the platform in Distance while calculating Time.

Should not consider the only Length of the platform(650 m).

Length of train = 240.
Time taken to travell the pole = 24sec.
So V = d/t.
= 240/24,
= 10m/s,

So time taken to travel 650m long platform is;
T = d/t.
= 650/10,
= 65sec(ans).

There is a way to solve like dis also
s=(D1+D2)/(t1+t2) i.e 10=(240+650)/(24+x).
In this way, we will get the answer 65.

Can anyone tell me, I am right or wrong?

I think 65 is correct.
A train 240 m long passes a pole in 24 seconds.
240 is the find measurement where you find the 1 m ratio.
How long will it take to pass a platform 650 m long?
Based on finding the 1 m ratio. you have to find for 650 and that is why 65 is correct.

As the train crosses the platform, we have to add the length of the train to the platform length. (remember this the train engine is at the platform starting point).

By using the pole concept in the given problem we can find the speed of the train.

Speed=distance*time.

240/24=10sec.

Because, the train to cross the platform, the total length travelled to cross the platform is equal to the length of the train plus length of the platform,

Speed= (240+650) /10.
= 890/10.
= 89.

As the train has to pass the platform its length need to be considered so they added 240 to the platform length.