Abdul, while driving to school, computes the average speed for his trip to be 20 km/h. On his return trip along the same route, there is less traffic and the average speed is 40 km/h. What is the average speed for Abdul’s trip?

Given: $\mathrm{V} =\mathrm{ }20 \mathrm{km}/\mathrm{h}, \mathrm{v} =\mathrm{ }40 \mathrm{km}/\mathrm{h}$
Let the distance between Abdul’s home to his school be S.
Time taken to reach the school, 

${\mathrm{t}}_1=\frac{\mathrm{S}}{\mathrm{V}}$$=\frac{\mathrm{S}}{20} \mathrm{hr}$
Time taken to reach home from the school, 

${\mathrm{t}}_2=\frac{\mathrm{S}}{\mathrm{V}}$$=\frac{\mathrm{S}}{40} \mathrm{hr}$
Therefore, the time taken to complete the trip, ${\mathrm{t}}_{\mathrm{total}}=\mathrm{ }\frac{\mathrm{S}}{20}+\frac{\mathrm{S}}{40}$
$=\frac{3\mathrm{S}}{40} \mathrm{hr}$
Total distance traveled during the trip = 2S
Therefore, the average speed for Abdul’s trip $=\frac{\mathrm{Total} \mathrm{distance}}{\mathrm{Total} \mathrm{Time}}$

$=\frac{2\mathrm{S}}{3\mathrm{S}}\times 40$

$=26.67 \mathrm{km}/\mathrm{hr}$

The average speed of Abdul’s trip is $26.67 \mathrm{km}/\mathrm{hr}$.