The ratio between the speeds of two trains is 7 8 If the second train runs 420 km in 4 hours T...........

Quantitative Aptitude (CDS) Time & distance

The ratio between the speeds of two trains is 7:8.If the second train runs 420 km in 4 hours .Then the time taken to cross a bridge 100 m by first train is?

2 sec

3 sec

3.19 sec

5 sec

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Explanation:

second train speed is=420/4
=105 km/h
ratio is=7/8
7/8 =v/105
v=7× 105/8 km/h
first train speed is =735/8 km/h
bridge length is=100/1000 km
time=100/1000×(735/8)
=8/7350 hour
=3.91 second