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Aptitude - Problems on Trains - Discussion

Discussion Forum : Problems on Trains - General Questions (Q.No. 20)
Problems on Trains
20.
A train moves past a telegraph post and a bridge 264 m long in 8 seconds and 20 seconds respectively. What is the speed of the train?
69.5 km/hr
70 km/hr
79 km/hr
79.2 km/hr
Answer: Option
Explanation:

Let the length of the train be x metres and its speed by y m/sec.

Then, x = 8     =>     x = 8y
y

Now, x + 264 = y
20

=> 8y + 264 = 20y

=> y = 22.

Therefore Speed = 22 m/sec = ( 22 x 18 ( km/hr = 79.2 km/hr.
5

Discussion:
46 comments Page 3 of 5.
Vamsy said:   1 decade ago
@Hussaian.

1) km/hr to m/s conversion:
km/hr = a x 5km/18hr.

2) m/s to km/hr conversion:
m/s = a x 18km/5hr.
Diksha rajput said:   7 years ago
It can be done directly.

D=264m T= (20-8) =12 s.
S=D/T =264/12 =22.
Converting it into kmph.
22*18/5=79.2.
Manu said:   8 years ago
We directly do speed=264/12.
=22*18/5. And we get the answer.
Pavan said:   1 decade ago
Why we didn't add time. While calculating the speed. We taken only 20. Why we didn't take 20+8?
Angel said:   1 decade ago
Hey can anyone tell me instead of taking x/y=8 , Can we take x/y=20 because it is also time ?
Raghavi said:   9 years ago
I am not getting the answer when we proceed it with the same step as the previous problem.
Ravibhai said:   2 years ago
Simple:

Time = Distance/Speed.
Speed = Distance/Time.
= 264/(20-8)×5/18.
= 79.2km/h.
(18)
Govindraj said:   6 years ago
Hi all,

22 m/s = 22*1000/3600 km/hr = 6.1 km/hr.

Let me know if I am wrong.
(2)
Ginil kumar said:   7 years ago
@Rana Sk.

This is the simple way to get this answer. Thanks for explaining.
Rakshi said:   9 years ago
Hi, I can't understand. Why are we taking time as the difference of both?
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