Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 19)
19.
A train speeds past a pole in 15 seconds and a platform 100 m long in 25 seconds. Its length is:
Answer: Option
Explanation:
Let the length of the train be x metres and its speed by y m/sec.
| Then, | x | = 15  y = |
x | . |
| y | 15 |
 |
x + 100 | = | x |
| 25 | 15 |
15(x + 100) = 25x
15x + 1500 = 25x
1500 = 10x
x = 150 m.
Discussion:
55 comments Page 6 of 6.
S Madhukar said:
1 decade ago
Speed = Length/Time.....(1).
Distance = Speed*Time.....(2).
Time = Higher time - Lower time.
= 25-15 = 10.
Distance = 100 given.
100 = Speed*10.
Speed = 10 substitute in equation (1).
Length = 10*15 = 150.
Distance = Speed*Time.....(2).
Time = Higher time - Lower time.
= 25-15 = 10.
Distance = 100 given.
100 = Speed*10.
Speed = 10 substitute in equation (1).
Length = 10*15 = 150.
Amit said:
1 decade ago
Why 25-10?
Anishghoshroy said:
1 decade ago
Let the speed of the train be x.
Then, the length of the train is 15x.
Therefore, 100+15x = 25x.
x = 10.
Which mean the speed of the train is 10 m/s as assumed above.
Then the length of train is 150 m.
Then, the length of the train is 15x.
Therefore, 100+15x = 25x.
x = 10.
Which mean the speed of the train is 10 m/s as assumed above.
Then the length of train is 150 m.
Kiranjit Misra said:
1 decade ago
Let speed = X; then length of train = 15 X;
Hence (15X+100)/X = 25.
Answer the length of train is 15X = 10*15 = 150.
Hence (15X+100)/X = 25.
Answer the length of train is 15X = 10*15 = 150.
Samarpita Guha said:
10 years ago
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.
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.
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