SOLUTION: a train 100 metre long running at 54 km /hr takes 20 seconds to pass a bridge..the lenght of bridge is ?

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Question 860246: a train 100 metre long running at 54 km /hr takes 20 seconds to pass a bridge..the lenght of bridge is ?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +L+ = the length of the bridge in km
+L%2F.1+ = the number of times the train would fit
into the bridge
+L%2F.1+%2B+2+ = the number of times the entire train
fits in order to "pass through"
( note that I need the +2+ to account for both
head and tail to get in and also to get out )
+%28%28+L%2F.1+%2B+2+%29%2A.1+%29+%2F+54+=+20+%2F+3600+
++L+%2B+.2+=+54%2A%28+1%2F180+%29+
+L+=+.3+-+.2+
+L+=+.1+ km
The bridge is 100 m long
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check:
The train travels 3 of it's lengths or .3 km
to pass through
+.3+%2F+54+=+.1%2F18+ hrs
+%28+1%2F180+%29%2A3600+=+20+ sec
OK
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Hope I got it, and hope it's
not confusing