Given: Speed while going = 40 km/hr Decrease in speed while returning = 20% Formula used: Average speed when distance covered is same = 2xy/(x+y) Where, x = Speed while going y = Speed while returning Calculation: Speed while returning =40×[(100–20)/100] km/hr ⇒40×(80/100) km/hr ⇒ 32 km/hr Now, average speed =(2×40×32)/(40+32) km/hr ⇒(80×32)/72 km/hr ⇒ 35.56 km/hr ∴ The average speed of the whole journey is 35.56 km/hr