A car moves from `X` to `Y` with a uniform speed `v_u` and returns to `Y` with a uniform speed `v_d`. The average speed for this round trip is :

Options

A. `(v_(1)+v_(2))/2`
B. `sqrt(v_(1)v_(2))`
C. `(v_(1)v_(2))/(v_(1)+v_(2))`
D. `(2v_(1)v_(2))/(v_(1)+v_(2))`

Answer

D

Explanation

Average speed`= (d+d)/(d/v_(1)+d/v_(2))=(2v_(1)v_(2))/(v_(1)+v_(2))`