Aptitude::Time and Distance
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Important Formulas 
Speed = ( Distance / Time ), Time = ( Distance / Speed ), Distance = ( Speed * Time ) 

1.  x km/hr = [ x * 5/18 ] m/sec. 
2.  If the ratio of the speeds of A and B is a : b, then the ratio of the times taken by them to cover the same distance is 1/a : 1/b or b : a. 
3.  x m/sec = [ x * 18/5 ] km/hr. 
4.

Suppose a man covers a certain distance at x km/hr and an equal distance at y km/hr. then, the average speed during the whole journey is [ 2xy / (x+y) ] km/hr.
