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

Let the school be at a distance of x km. If

t₁ is the time taken to reach the school, then

`t_1 = "distance"/"average speed" = x/20`

If t₂ is the time taken to reach back, then

`t_2 = "distance"/"average speed" = x/30`

Total time,

t = `t_1 + t_2`

= `x/20 + x/30 `

= `x [1/20 + 1/30]`

= `(5x)/60`

= `x/12`

Total distance x + x = 2x

Average speed = `"total distance"/"total time"`

= `(2x)/(x/12)`

= 24 km h^-1