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.
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.
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)
Preeti2009_delhi@yahoo.com said:
1 decade ago
x is the velocity of the train?125/7=17.85=velocity of the =x, in the second case,
While in the 1st case there is the tree thats why we will consider only the lengh of the train and actually we do not know that?
According to the 1st case speed of the train will be =l/13.
How we can say that the speed of the train is I,II?
While in the 1st case there is the tree thats why we will consider only the lengh of the train and actually we do not know that?
According to the 1st case speed of the train will be =l/13.
How we can say that the speed of the train is I,II?
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.
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.
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.
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.
Chiku said:
1 decade ago
Here we assume that speed is x in both the cases and we just equate the two equation.
Kab said:
5 years ago
Option B be possible because the third equation involves the relative speed.
(1)
Jessy said:
1 decade ago
Sorry I'm not clear with 125/7 please explain it. Thank you.
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