Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 3)
3.
The length of the bridge, which a train 130 metres long and travelling at 45 km/hr can cross in 30 seconds, is:
Answer: Option
Explanation:
| Speed = |  |
45 x | 5 |  m/sec |
= | |
25 | m/sec. |
| 18 | 2 |
Time = 30 sec.
Let the length of bridge be x metres.
| Then, | 130 + x | = | 25 |
| 30 | 2 |
2(130 + x) = 750
x = 245 m.
Video Explanation: https://youtu.be/M_d8WufJWKc
Discussion:
249 comments Page 15 of 25.
Nitin said:
1 decade ago
Why we are subtracting 130 from 375. While train runs on the bridge not off the bridge?
Murugan said:
1 decade ago
@Nithin.
Distance = speed x time.
So distance = 45*5/18*30.
Distance = 375 (this is the length of both train+bridge).
So we have to subtract train length (130 m).
Distance = 245.
Distance = speed x time.
So distance = 45*5/18*30.
Distance = 375 (this is the length of both train+bridge).
So we have to subtract train length (130 m).
Distance = 245.
Siva Nandi Reddy said:
1 decade ago
Train length and bridge length is always add thats why we subtracted 130 from 375?
Pranil T. Mhatre said:
1 decade ago
Speed of the Train = 45 km/hr.
Speed of the train in meters/sec = (45*1000)/(60*60) = (25/2).
Distance covered by train in 30 secs = (25/2)*30 = 375 meters.
Now the train having the length 130 meters had crossed the bridge in 30 secs so the length of the Bridge = 375 - 130 = 245 meters.
Speed of the train in meters/sec = (45*1000)/(60*60) = (25/2).
Distance covered by train in 30 secs = (25/2)*30 = 375 meters.
Now the train having the length 130 meters had crossed the bridge in 30 secs so the length of the Bridge = 375 - 130 = 245 meters.
Suren said:
1 decade ago
@Sai.
Your method is fantastic and very easy to understand. Great job! keep it up man. Thanks!
Your method is fantastic and very easy to understand. Great job! keep it up man. Thanks!
SK Lodhi said:
1 decade ago
130+B = 30 Sec.*45*5/18 m/s(time*speed).
130+B = 375 m.
Where B = length of the Bridge = 375 - 130 = 245 meters.
130+B = 375 m.
Where B = length of the Bridge = 375 - 130 = 245 meters.
Radha said:
1 decade ago
Please explain method clearly how we will dot 750?
Safina M said:
1 decade ago
Hey Radha,
Cross multiply (139+x)/30=25/2 i.e,
2*(130+x)=30*25.
i.e., 260+2x=750.
2x=750-260.
2x=490.
x=490/2.
Hence, x=245.
Cross multiply (139+x)/30=25/2 i.e,
2*(130+x)=30*25.
i.e., 260+2x=750.
2x=750-260.
2x=490.
x=490/2.
Hence, x=245.
Varalakshmi saravanan said:
1 decade ago
Hi Friends it's very simple.
Length of the Train = 130 m.
Speed = 45 km/hr after converting into m/s we will get (45*5/18) => 25/2.
Time = 30 sec.
Length of bridge = x + length of train.
X+length of train = Speed of the train*time.
X+130 = 25/2*30.
X+130 = 375.
X = 375-130.
X = 245.
Length of the Train = 130 m.
Speed = 45 km/hr after converting into m/s we will get (45*5/18) => 25/2.
Time = 30 sec.
Length of bridge = x + length of train.
X+length of train = Speed of the train*time.
X+130 = 25/2*30.
X+130 = 375.
X = 375-130.
X = 245.
Deep said:
1 decade ago
Easy method is by using time and distance formula.
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