A car moves from X to Y with a uniform speed vu and returns

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

Average speed =	total distance travelled
	total time taken

Let s be the distance from X to Y.

∴ Average speed =	s + s	=	2s
	t₁ + t₂		s/v_u + s/v_d