Question

Hey brainly users !
plz answer it ....

Answer 1

Let the Total Distance travelled by the car be : D

Distance Travelled during the 1st Part is D/3

Speed of the car during the 1st Part of the Journey = 20 km/hr

We know that Speed is Ratio of Distance travelled to that of Time taken

⇒ Time taken is the Ratio of Distance travelled to that of Speed

⇒ Time taken to travel the 1st Part of the journey = (D/3)/20 = (D/60) hr

Distance Travelled during the 2nd Part is D/3

Speed of the car during the 2nd Part of the Journey = 30 km/hr

⇒ Time taken to travel the 2nd Part of the journey = (D/3)/30 = (D/90) hr

Distance Travelled during the 3rd Part is D/3

Speed of the car during the 3rd Part of the Journey = 60 km/hr

⇒ Time taken to travel the 3rd Part of the journey = (D/3)/60 = (D/180) hr

We know that Average speed is given by the Ratio of Total Distance Travelled to that of Total Time Taken.

Total Distance Travelled  = (D/3 + D/3 + D/3) = D

Total Time Taken = (D/60 + D/90 + D/180) = D/30

So The  Average speed of the Car is (D)/(D/30) = D × (30/D) = 30 km/hr

Answer 2

Let total distance = 3s

The average speed is defined as

Average speed = total distance covered/ time taken

first 1/3 part or S part is covered with speed 20kmph.

So time taken to cover first s part = t1 =distance /speed = s/20

similarly , time taken to cover second s part=t2 = s/30

t3 = s/60

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So total time = t1+t2+t3 = s/20 +s/30 + s/60 = 6s/60 =s/10

And total distance covered = 3s

So average speed = 3s/(s/10) = 30kmph