Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 16)
16.
A train travelling at a speed of 75 mph enters a tunnel 3
miles long. The train is 
mile long. How long does it take for the train to pass through the tunnel from the moment the front enters to the moment the rear emerges?
miles long. The train is mile long. How long does it take for the train to pass through the tunnel from the moment the front enters to the moment the rear emerges?Answer: Option
Explanation:
| Total distance covered |
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 Time taken |
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| = 3 min. |
Discussion:
130 comments Page 5 of 13.
Ishant said:
1 decade ago
According to me answer will be c)3.2min
Because the lenth of train has to be taken twice bec. intially train of length 1/4 will enter and then it wil leave the tunnel
Therefore distance travelled=7/2+1/4+1/4=4
Please check it out
Because the lenth of train has to be taken twice bec. intially train of length 1/4 will enter and then it wil leave the tunnel
Therefore distance travelled=7/2+1/4+1/4=4
Please check it out
Nidhi said:
1 decade ago
Time=Distance/velocity ---------------------(1)
time=(15/75*4)=1/20 hrs ---------------------(2)
time=(1/20)*60=3 min ---------------------(3)
I understand all these statement, but i have problem. with the statement (2) that how we just find out the time without converting meter into miles or vice versa. In this they simply find the time without any conversion and it is not so acceptable
Please clear me out..
time=(15/75*4)=1/20 hrs ---------------------(2)
time=(1/20)*60=3 min ---------------------(3)
I understand all these statement, but i have problem. with the statement (2) that how we just find out the time without converting meter into miles or vice versa. In this they simply find the time without any conversion and it is not so acceptable
Please clear me out..
Amit said:
1 decade ago
Actually time and distance two different units.we want to find the time of crossing the tunnel. Speed is given in the form of 75 miles/hour so our concern only with hour not distance so change hour to minute and then calculate ur answer.
Total length =7/2 + 1/4 = 15/4 miles
Speed = 75 mile/hour = (75/60)miles/minute
Now time taken is distance / speed = (15/4) / (75/60) = 15*60/4*75 =3 minute.
Total length =7/2 + 1/4 = 15/4 miles
Speed = 75 mile/hour = (75/60)miles/minute
Now time taken is distance / speed = (15/4) / (75/60) = 15*60/4*75 =3 minute.
Shro said:
1 decade ago
Guys for those who asked doubt here is the answer.
Its given in miles per hour and we have to find time in minutes.
So no need to convert into any other form.
Its given in miles per hour and we have to find time in minutes.
So no need to convert into any other form.
Shro said:
1 decade ago
As per the given question:
tunnel's length is 3(1/2) i.e. = 7/2
train's length is 1/4.
So as per the formulas we are supposed to add lengths so we add (7/2)+(1/4)
tunnel's length is 3(1/2) i.e. = 7/2
train's length is 1/4.
So as per the formulas we are supposed to add lengths so we add (7/2)+(1/4)
Shro said:
1 decade ago
Distance is (7/2 ) + (1/4 ) = (15/4)
speed is 75mph
time= distance /speed
So time= (15/4) / 75
which can also be written as ( 15/(75*4))
So we get it as 1/20 hrs
But expected ans is in minutes.
So convert hrs into minutes.
So (1/20) * 60
which gives the final answer 3min.
Good Luck :)
speed is 75mph
time= distance /speed
So time= (15/4) / 75
which can also be written as ( 15/(75*4))
So we get it as 1/20 hrs
But expected ans is in minutes.
So convert hrs into minutes.
So (1/20) * 60
which gives the final answer 3min.
Good Luck :)
Sudheer said:
1 decade ago
Given data is
Distance is (7/2 ) + (1/4 ) = (15/4)
Speed is 75mph
Formula for this is speed=(length/time) i.e.,Time=(length/speed)
Time=(15/4)/75=(15/(4*75))=3 mins
Distance is (7/2 ) + (1/4 ) = (15/4)
Speed is 75mph
Formula for this is speed=(length/time) i.e.,Time=(length/speed)
Time=(15/4)/75=(15/(4*75))=3 mins
Tarun said:
1 decade ago
@Nidhi, Shro.
If the tunnel lengh is given in KMPH, then we need to convert the speed also in KMPH, here tunnel length in mph, so we will keep the given speed mph as it is.
If the tunnel lengh is given in KMPH, then we need to convert the speed also in KMPH, here tunnel length in mph, so we will keep the given speed mph as it is.
Vinit said:
1 decade ago
In question it is asked that "How long does it take for the train to pass through the tunnel from the moment the front enters to the moment the rear emerges?" so 1/4 will be added twice i.e.
Total distance would be 7/2 + 1/4 + 1/4
And Finally answer is 3.2 mins
Total distance would be 7/2 + 1/4 + 1/4
And Finally answer is 3.2 mins
Jaani said:
1 decade ago
@vinit: Nope! Look, we need to calculate time taken by the train to cover the "inside" of the tunnel :
1)When "Front emerges".. no part of the train is 'inside' the tunnel.. therefore distance covered till nw = 0
2) when the front emerges out.. it has covered the whole distance of the tunnel = 7/2
3) rest of the train is still inside the tunnel (as only the front has emerged out).. so now the remaining train comes out.. Hence 7/2 + 1/4
1)When "Front emerges".. no part of the train is 'inside' the tunnel.. therefore distance covered till nw = 0
2) when the front emerges out.. it has covered the whole distance of the tunnel = 7/2
3) rest of the train is still inside the tunnel (as only the front has emerged out).. so now the remaining train comes out.. Hence 7/2 + 1/4
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