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 31/2 miles long. The train is 1/4 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?
2.5 min
3 min
3.2 min
3.5 min
Answer: Option
Explanation:

Total distance covered
= ( 7 + 1 ( miles
2 4
= 15 miles.
4

Therefore Time taken
= ( 15 ( hrs
4 x 75
= 1 hrs
20
= ( 1 x 60 ( min.
20
= 3 min.

Discussion:
128 comments Page 1 of 13.

Suriya said:   4 months ago
@All.

Just add the distance, simply using the time formula. You get 0.05 hours just multiply 60 to get minutes. The answer is 3.
(1)

Sagnik Bhunia said:   9 months ago
Train length must be multiplied by 2 and added tunnel length to get the total distance as the problem says train starts from entering the tunnel from front to exiting the tunnel till its end.

Shouldn't it be the correct interpretation? Anyone, Please clarify.
(11)

Kolli Hemanth said:   1 year ago
@All.
Here mph means meters per hour but the distance is given in miles. So, miles must be converted into meters. 1 mile=1609 meters.
(13)

Muthumari said:   2 years ago
Speed = distance/time.
75/60(meter/min) = [ (7/2)+(1/4)] ÷ t.
t = (15/4)×(60/75),
t = 3min.
(2)

Harish said:   2 years ago
Train distance is in miles and speed is in meters without conversion of miles into meters how can we compare both?

Anyone, please clarify this.
(13)

Sravya Sree said:   2 years ago
@Atikraja.

It is a mixed fraction.
First, multiply 2(denominator)*3(first term numerator) = 6 then add 1 which is 7 and include the denominator as it is;
i.e 3*2+1=7/2.
(2)

Atikraja Khochikar said:   2 years ago
How 7/2 came? anyone explain me.
(6)

Shyam said:   3 years ago
The speed of the train = 75mph.
=75 * 1/60.
Train speed = 5/4seconds.

The total distance is (7/2 + 1/4),
= 15/4mile.

Formula of time = distance /speed.
= 15/4/5/4.
= 15/4 * 4/5.
= 3seconds.
(7)

Jahnavi said:   3 years ago
1meter = 0.0006 miles.

So, the conversion of meters to miles is not required.

You can directly calculate the time without changing units.

Note: The length of the train need not be taken twice. This is similar to the bridge problem (train crossing the bridge).
(5)

Shubham said:   3 years ago
Ans must be 3.2 min.

We have to take the length of train twice.
7/2 + 1/4 + 1/4 = 4 miles.
Then,
Time = 4/75.
=0.05333 hr.
In seconds 0.05333*60= 3.198 which is 3.2 min.
(23)


Post your comments here:

Your comments will be displayed after verification.