Question

a motorcyclist drives from A to B with a uniform speed of 30 km per hour and returns back with a speed of 20 km per hour. find its average speed.
Plz Tell me according to 9th class.

Answer 1

$\textbf{Answer}$

Suppose the distance from point A to B is x km
$\textbf{Time = Distance/Speed}$

$\textbf{Travelling from point A to B -}$
Speed,S1 = 30 km/hour
Distance = x km
Time taken,T1 = x/30 hour

$\textbf{Travelling from point B to A -}$
Speed,S2 = 20 km/hour
Distance = x km
Time taken,T2 = x/20 hour

$\textbf{Total journey from point A to B}$ and $\textbf{from Point B to A -}$
Total Distance,S = x+ x = 2x km
Total Time = T1 + T2
=> Total Time = (x/30) + (x/20) hour

=> $\textbf{Average Speed}$ = $\textbf{ Total Distance/Total Time}$

=> Average Speed = (2x)/{(x/30) + (x/20)}

=> Average Speed = (2x)/{(50x)/(30×20)}

=> Average Speed = (2×30×20)/(50)

=> Average Speed = 2×6×2 = 24

$\textbf{Average Speed = 24 km/hour}$

$\textbf{Hope My Answer Helped}$
$\textbf{Thanks}$

Answer 2

$\textbf{let's assume that the body covers}$

$\textbf{the distance from A to B}$

$\textbf{Let the distance between those two points be d}$

$\textbf{Speed1 = 30km/h(given)}$

$\textbf{Time1 = distance / speed}$

$\textbf{= d/30 h}$

$\textbf{Speed when he is returning = 20km}$

$\textbf{Time2 = d/20 h}$

$\bf{Time2 = \frac{d}{20h}}$

$\textbf{Average speed = total distance covered / total time taken}$

$\mathbf{=( d+d) ÷ (d/20) +(d/30)}$

$\mathbf{= 2d ÷ (3d+2d) / 60}$

$\mathbf{= (12)(2)}$

$\mathbf{= 24}$

$\textbf{So, the average speed is 24 km/h.}$

$\bf{Thanks}$

$\bf{Have a colossal day ahead}$

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