Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 17)
17.
A train 800 metres long is running at a speed of 78 km/hr. If it crosses a tunnel in 1 minute, then the length of the tunnel (in meters) is:
Answer: Option
Explanation:
| Speed = |  |
78 x | 5 |  |
m/sec | = | |
65 | |
m/sec. |
| 18 | 3 |
Time = 1 minute = 60 seconds.
Let the length of the tunnel be x metres.
| Then, | |
800 + x | |
= | 65 |
| 60 | 3 |
3(800 + x) = 3900
x = 500.
Discussion:
54 comments Page 2 of 6.
Adnan said:
6 years ago
To understand why we use 5/18 so i clarify that to convert km into m we multiply with 1000 and from hours to second we divided by 60*60.
Hence we get 5/18.
Suppose to change 1 km /hr into metre /sec.
1 * 1000/60 * 60 = 5/18.
Hence we get 5/18.
Suppose to change 1 km /hr into metre /sec.
1 * 1000/60 * 60 = 5/18.
(2)
ABDUL WAHAB SHAH said:
6 years ago
Last step:
3(800 + x) = 3900.
2400 + 3x = 3900.
3x = 3900 - 2400.
3x = 1500.
x = 1500/3.
x = 500.
3(800 + x) = 3900.
2400 + 3x = 3900.
3x = 3900 - 2400.
3x = 1500.
x = 1500/3.
x = 500.
(5)
Rohan said:
7 years ago
Why need to convert 1 minute to 60 seconds?
Naveen said:
7 years ago
X+800 = 78 * 5/18 * 60,
X+800 = 13*5/3 *60,
X+800 = 13*5*20,
X+800 = 65*20,
X+800 = 1300,
X = 1300-800,
X = 500.
X+800 = 13*5/3 *60,
X+800 = 13*5*20,
X+800 = 65*20,
X+800 = 1300,
X = 1300-800,
X = 500.
Yt prasad said:
7 years ago
65/3 * 60 = 65 * 20 = 1300 - 800 = 500.
(2)
Roobha said:
7 years ago
1km = 1000m,
1hr = 3600sec.
Convert,
Km/hr=m/sec.
= 1000/3600m/sec,
= 5/18m/sec.
1hr = 3600sec.
Convert,
Km/hr=m/sec.
= 1000/3600m/sec,
= 5/18m/sec.
Arushi said:
7 years ago
I am not getting, how come 5/18? Please, someone explain me.
Sasinrit said:
7 years ago
Speed =78000/3600=1300/min.
Length of tunnel=1300-800=500.
Length of tunnel=1300-800=500.
(1)
Sarang said:
8 years ago
Distance =speed * time,
D=78km/h*1minute,
D=78*5/18*60.
D=78*.277*60.
D=21.6*60= 1300-800= 500.
D=78km/h*1minute,
D=78*5/18*60.
D=78*.277*60.
D=21.6*60= 1300-800= 500.
Naman said:
8 years ago
What if we turn the speed into m/s first, like.
78 x (5/18)=> 65/3 => 15,
then use formula D = S*T.
then we get,
D+800 = 15 * 60.
D+800 = 900,
D = 100,
Is this wrong ?
why 2 different answer?
78 x (5/18)=> 65/3 => 15,
then use formula D = S*T.
then we get,
D+800 = 15 * 60.
D+800 = 900,
D = 100,
Is this wrong ?
why 2 different answer?
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