Aptitude Hack#86(20-5-19)

Question:

 A man is standing on a railway bridge which is 180 m long. He finds that a train crosses the bridge in 20 seconds but himself in 8 seconds. Find the length of the train and its speed?

   A )   52 km
   B )   53 km
   C )   54 km
   D )   55 km

Answer: C) 54 km

Explanation:
 Let the length of the train be x metres,

Then, the train covers x metres in 8 seconds
 and (x + 180) meters in 20 sec

=> x/8=(x+180)/20 
=> 20x = 8 (x + 180)      
 <=>      x = 120.

Length of the train = 120 m.

Speed of the train = (120/8) m / sec 
 = (15 *18/5) kmph = 54 km