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:
126 comments Page 1 of 13.

Kolli Hemanth said:   6 months 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.
(2)

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

Harish said:   7 months 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.
(4)

Sravya Sree said:   1 year 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:   1 year ago
How 7/2 came? anyone explain me.
(4)

Shyam said:   2 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.
(4)

Jahnavi said:   2 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).
(3)

Shubham said:   2 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.
(16)

Kishan Maurya said:   2 years ago
Length of train will be 2 times of 1/4.
And correct ansr is 3.2min.
(4)

Arbaj Tamboli said:   2 years ago
75 mph means 75 miles per hour.
(3)


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