Question

A motorcyclist drives from A to B with a uniform speed of 30 km h–1 and
returns back with a speed of 20 km h–1. Find its average speed.
​

Answer 1

Answer:

24 km/h

Explanation:

Given:

• Uniform speed from A to B = 30 km/h

• Speed while returning back from B to A =  20 km/h

To find:

• Average speed of the motorcyclist

Average speed = $\frac{Total \ distance }{Total \ time}$

Let distance from a to b = x

Total distance = X+X = 2X

Time = $\frac{Distance}{Speed}$

Time while going from A to B = $\frac{x}{30}$

Time while coming back from b to a = $\frac{x}{20}$

Average speed = $\frac{2x}{\frac{x}{30}+\frac{x}{20} }$

Average speed =$\frac{2x}{\frac{2x}{60}+\frac{3x}{60} }$

Average speed = $\frac{2x}{\frac{5x}{60} }$

Average speed = $\frac{2}{5} \times 60$

Average speed = 2×12

Average speed = 24 km/h

The average speed of the motorcycle is equal to 24 km/h

Answer 2

GIVEN:

• Motorcyclist drives from A - B with a constant speed of 30 km/h
• And returning with a spee d of 20 km/h

TO FIND:

• Average speed of motorcyclist

SOLUTION:

Let

• Distance from A - B = x
• Similarly , B - A = x
• Total distance = AB + BA = x + x = 2x

Total speed = 30 + 20 = 50 km/h

We know that

Time = distance/speed

Total Time = x/30 + x/20 = 5x/60 = x/12

Average speed = Total distance/Time

Substituting the values we have

Avg speed = 2x/x/12

Avg speed = 2 × 12

Average speed = 24 km/h

Hence , Average speed of motorcyclist = 24km/h