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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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