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 40 km `h^(-1)`. What is the average speed for Abdul's trip ?

Explanation

Let one way distance =x km
Time taken while driving to school = `t_1` hour
Time taken during the return trip= `t_2` hour
Now, time = `("distance")/("average speed")`
`thereforet_1=x/20` hour
and `t_2=x/40` hour
`therefore` Average speed for Abdul.s trip
`=("Total distance travelled")/("Total time taken")`
`=(x+x)/(t_1+t_2)`
`=(2x)/(x/20+x/40)kmh^(-1)`
`=(2x)/((2x+x)/40)kmh^(-1)`
`=(2x)/(3x)xx40kmh^(-1)`
`=2/3xx40kmh^(-1)`
=`80/3kmh^(-1)`
`=26.67kmh^(-1)`