Question

Motorcyclist drives from a to b with the uniform speed of 30 km per hour and returns back with the speed of 20 km per hour find the average speed

Answer 1

Let the distance from A to B is 's'.

From A to B,

Distance = s

Average speed = 30 km/h

Using formula,

⇒ Average Speed = Distance ÷ Time

⇒ 30 km/h = s ÷ Time

•°• Time = sh / 30 km

From B to A,

Distance = s

Average Speed = 20 km/h

Using formula,

⇒ Average Speed = Distance ÷ Time

⇒ 20 km/h = s ÷ Time

•°• Time = sh / 20 km

Now, to find the average speed of total journey,we need total distance travelled and total time taken.

Total Distance = s + s = 2s

Total Time = ( sh/30 km ) + ( sh/20 km )

= ( 2sh + 3sh ) / 60 km

= ( 5sh ) / 60 km

= sh/12 km

Using formula,

⇒ Average Speed = Total Distance ÷ Time taken

= ( 2s ) ÷ ( sh/12 km )

= ( 2s ) × ( 12 km ) × ( 1/sh )

= 24 km/h

Hence, the average speed of total journey is 24 km/h.

Answer 2

Answer:

24 km./hr.

Hope it helps.