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# A boy walks to his school at a distance of 6 km with constant speed of 2.5 km/hr and walks both with a constant speed of 4 km/hr . His average speaks for the round trip is

$\begin{array}{1 1} (a) \;24/13\;km/hr \\ (b) \;40/13\;km/hr \\ (c) \;3\;km/hr \\ (d) \;\frac{1}{2}\;km/hr\end{array}$

Average speed $= \large\frac {Total\; distance }{Total\; time \;taken}$
time taken for forward $=\large\frac{Distance}{speed}=-\frac{6}{2.5}$
Time taken for return trip $= \large\frac{6}{4}$
Average speed = $\large\frac{6+6}{\large\frac{6}{2.5}+\frac{6}{4}}$
$\qquad= \large\frac{40}{13}\;km/hr$