A constant distance from Chennai to Bangalore is covered

A constant distance from Chennai to Bangalore is covered by Express train at 100 km/hr. If it returns to the same distance at 80 km/hr, then the average speed during the whole journey is

If same distance are covered at two different speed of x and y kmph, the average speed of journey

=	2xy
	x + y

=		2 × 100 × 80		kmph
		100 + 80

= 88.89 kmph