A boy walks to his school at a distance of $6\, km$ with constant speed of $2.5\, km/hour $ and walks back with a constant speed of $4 \,km/hr.$ His average speed for round trip expressed in $km/hour$, is
A boy walks to his school at a distance of $6\, km$ with constant speed of $2.5\, km/hour $ and walks back with a constant speed of $4 \,km/hr.$ His average speed for round trip expressed in $km/hour$, is
$24/13$
$40/13$
$3$
$1/2$
A boy walks to his school at a distance of $6\, km$ with constant speed of $2.5\, km/hour $ and walks back with a constant speed of $4 \,km/hr.$ His average speed for round trip expressed in $km/hour$, is
Distance average speed $ = \frac{{2{v_1}{v_2}}}{{{v_1} + {v_2}}}$$ = \frac{{2 \times 2.5 \times 4}}{{2.5 + 4}}$
$ = \frac{{200}}{{65}} = \frac{{40}}{{13}}km/hr$
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