Question

Abdul, while driving to school, computes the average speed for his trip to be 20 km h-1. On his return trip along the same route, there is less traffic and the average speed is 30 km h-1. What is the average speed for Abdul's trip?

Answer 1

AnSwer :

The average speed for Abdul's trip is 24 km/h.

SoLution :

◑ Let the school be at a distance of $\rm{x}$ km. If $\rm{t_1}$ is time taken to reach the school.

$\leadsto\sf{t_1 = \dfrac{distance}{average\:speed} = \dfrac{x}{20}}$

◑ If $\rm{t_2}$ is time taken to reach back, then

$\leadsto\sf{t_2 = \dfrac{distance}{average\:speed} = \dfrac{x}{30}}$

◑ Total time, $\rm{t = t_1 + t_2}$

= $\rm{\dfrac{x}{20} + \dfrac{x}{40}}$

= $\rm{x [\dfrac{1}{20} + \dfrac{1}{30}]}$

= $\rm{\dfrac{5x}{60}}$

= $\boxed{\rm \dfrac{x}{12}}$

◑ Total distance = $\rm{x + x = 2x}$

$\leadsto\sf{\dfrac{total\:distance}{total\:time} = \dfrac{2x}{x/12}}$

= $\boxed{\bf 24\: km/h}$

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