Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - Data Sufficiency 2 (Q.No. 2)
Directions to Solve
Each of the questions given below consists of a question followed by three statements. You have to study the question and the statements and decide which of the statement(s) is/are necessary to answer the question.
2.
What is the speed of the train? | |
I. | The train crosses a tree in 13 seconds. |
II. | The train crosses a platform of length 250 metres in 27 seconds. |
III. | The train crosses another train running in the same direction in 32 seconds. |
Answer: Option
Explanation:
Let the speed of the train be x metres/sec.
| Time taken to cross a tree = | Length of the train |
| Speed of the train |
| Time taken to cross a platform = | (Length of the train + Length of the Platform) |
| Speed of the train |
| I gives, 13 = | l |  13x. |
| x |
| II gives 27 = | l + 250 |
| x |
| |
13x + 250 | = 27 |
| x |
| x = |
125 | m/sec. |
| 7 |
Thus I and II give the speed of the train.
The correct answer is (A.)
Discussion:
13 comments Page 1 of 2.
Yatendra said:
3 years ago
Why we have assumed here that the length of the train is equal to the length of the tree?
Please explain me.
Please explain me.
Kab said:
5 years ago
Option B be possible because the third equation involves the relative speed.
(1)
Kab said:
5 years ago
I think option B is correct.
(2)
Nikitha said:
5 years ago
How come 125/7?
Piklla ganesh said:
6 years ago
Option 3 is not possible, as we will have more variables and only one equation. The length of the first is in a variable, length of 2nd again.
You will have to assume relative speed, which will again be a variable. We are supposed to find the speed of train 1, which we won't be able to calculate.
You will have to assume relative speed, which will again be a variable. We are supposed to find the speed of train 1, which we won't be able to calculate.
Shubham said:
8 years ago
Option 3 is not possible, as we will have more variable and only 1 equation. The Length of the first train is in a variable, length of 2nd again.
You will have to assume relative speed, which will again be a variable. We are supposed to fine the speed of train 1, which we won't be able to calculate.
You will have to assume relative speed, which will again be a variable. We are supposed to fine the speed of train 1, which we won't be able to calculate.
Lakshmi said:
9 years ago
Why can't be option 3? Can anyone explain.
Shinde said:
9 years ago
1. Let the speed of the train be x metres/sec.
Velocity = length/time Therefore, time = length/speed.
Length of train = speed*time
= 13*x...................................(1).
2. Time=(length of train+length of platform)/speed of train,
27 = (length+250)/x.
= (13x+250)/x (from 1).
= 17.85 m/sec.
Because of that I & II correct
Velocity = length/time Therefore, time = length/speed.
Length of train = speed*time
= 13*x...................................(1).
2. Time=(length of train+length of platform)/speed of train,
27 = (length+250)/x.
= (13x+250)/x (from 1).
= 17.85 m/sec.
Because of that I & II correct
(1)
Nischal said:
1 decade ago
@Syed I want to add here one thing, in given example we have tree which is being crossed by the train. As per your explanation width of the tree should be 0/1 meter.
Syed said:
1 decade ago
Assume Speed of the train as "x".
So,
Case I: length of the train = speed*time.
= 13*x.
Case II:
length of the train+length of the platform = 27.
-------------------------------------------
speed of the train
13x(from case I) + 250 = 27.
-----------------------
x
x = 125/7 m/sec.
Thus I and II give the speed of the train.
So,
Case I: length of the train = speed*time.
= 13*x.
Case II:
length of the train+length of the platform = 27.
-------------------------------------------
speed of the train
13x(from case I) + 250 = 27.
-----------------------
x
x = 125/7 m/sec.
Thus I and II give the speed of the train.
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