top button
Flag Notify
    Connect to us
      Site Registration

Site Registration

What is the length of the railway-bridge ?

+1 vote
119 views

Chetan walks over a railway-bridge. At the moment that he is just ten meters away from the middle of the bridge, he hears a train coming from behind. At that moment, the train, which travels at a speed of 90 km/h, is exactly as far away from the bridge as the bridge measures in length. Without hesitation, Chetan rushes straight towards the train to get off the bridge. In this way, he misses the train by just four meters! If Chetan had rushed exactly as fast in the other direction, the train would have hit him eight meters before the end of the bridge.
What is the length of the railway-bridge?

posted May 2, 2014 by anonymous

Share this puzzle
Facebook Share Button Twitter Share Button LinkedIn Share Button

1 Answer

0 votes

Let the length of the bridge be x meters.

Running towards the train, Chetan covers 0.5x-10 meters in the time that the train travels x-4 meters. Running away from the train, Chetan covers 0.5x+2 meters in the time that the train travels 2x-8 meters.

Because their speeds are constant, the following holds:

(0.5x-10) / (x-4) = (0.5x+2) / (2x-8)
which can be rewritten to

0.5x2 - 24x + 88 = 0
Using the quadratic formula we find that x=44, so the railway-bridge has a length of 44 meters.

answer May 7, 2014 by Mishthy Mukherjee



Similar Puzzles
0 votes

Charles walks over a railway-bridge. At the moment that he is just ten meters away from the middle of the bridge, he hears a train coming from behind. At that moment, the train, which travels at a speed of 90 km/h, is exactly as far away from the bridge as the bridge measures in length. Without hesitation, Charles rushes straight towards the train to get off the bridge. In this way, he misses the train by just four meters! If Charles would, however, have rushed exactly as fast in the other direction, the train would have hit him eight meters before the end of the bridge.

What is the length of the railway-bridge?

0 votes

It is a small town railway station and there are 25 stations on that line. At each of the 25 stations the passengers can get tickets for any of the other 24 stations. How many different kinds of tickets do you think the booking clerk has to keep?

...