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5a5. Time, Speed, Distance and Races: GMAT Math Tutorials

Distance = Speed × Time


e.g., A walks at 1m/s for 10 sec. Distance traveled = 1 ?10 = 10m



Average Speed


E.g. A person travels from A to B at a speed of 40 mph and returns at 60 mph Average speed for journey


Average Speed =

Relative Speed


Case I


     A   →  10mph


         |---------------------------------------------|


                                                                  B    →  5mph


If A and B are moving in the opposite direction i.e. towards each other. A would take less time to cross B than if B were stationary. This because B is making it easier by moving towards A.


Case II

     A   →  8mph


         |---------------------------------------------|


                                                                  B    →  5mph


If A and B are moving in the same direction, it would take more time for A to overtake B, because B is moving away from A.


In Case I the relative speed of A wrt B = 10 + 5 = 15mph


In Case II the relative speed of A wrt B = 8 - 5 = 3mph

 
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