Question

a car travels from A to B at a speed of 20 km/h and returns at a speed of 30 km/h the average speed of the car for the whole journey is ...

Answer 1

If

a= speed from point A to B

b= speed from point B to A

Average speed= 2*a*b/(a+b)

So according to that,

2*20*30/(20+30)= 24kmph is the answer.

Answer 2

Here's your answer!!

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Speed from A to B = 20km/h

Let the Distance be x.

So,

Time =Distance/Speed
$= > \frac{x}{20} h$
Speed from B to A =30km/h

Let the Distance be x.
So,

Time =
$= > \frac{x}{30} h$

Now,

Total distance travelled=x+x =2x

Total time taken =
$= > \frac{x}{20} + \frac{x}{30}$

$= > \frac{3x + 2x}{60}$

$= > \frac{5x}{60}$

We know that,

$average \: speed = \frac{total \: distance \: travalled}{total \: time \: taken}$

$= > \frac{2x}{ \frac{5x}{60} }$

$= > \frac{2x \times 60}{5x} \\ = > \frac{120x}{5x} \\ = > 24$

Hence,

The average speed of while journey is
24 km/h.

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Hope it helps you!! :)