A car covers half of its journey with a speed of `10ms^(-1)` and the other half by `20 ms^(-1)` . The average speed of car during the total journey is

Options

A. `70ms^(-1)`
B. `15ms^(-1)`
C. `13.33ms^(-1)`
D. `7.5ms^(-1)`

Answer

A, C

Explanation

Let x is the total distance
Time to cover 1st half `=(x//2)/(10)`
Time to cover 2nd half `=(x//2)/(20)`
Average speed `=(x)/((x)/(20)+(x)/(40))=(1)/(((3)/(40)))=13.33ms^(-1)`