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UPSC Prelims

Mathematics

Theme:

Speed, Time and Distance / गति, समय और दूरी

Q72 2020, Speed, Time and Distance

A car travels from a place X to place Y at an average speed of v km / hr from Y to X at an average speed of 2v km / hr again from X to Y at an average speed of 3v km / hr and again from Y to X at an average speed of 4v km / hr Then the average speed of the car for the entire journey

एक कार v km / hr की औसत चाल से स्थान X से स्थान Y तक यात्रा करती है, Y से X तक 2v km / hr की औसत चाल से, फिर X से Y तक 3v km / hr की औसत चाल से और फिर Y से X तक 4v km/hr की औसत चाल से यात्रा करती है। तो संपूर्ण यात्रा के लिए कार की औसत चाल

Explanation Please wait..

Let the distance between X and Y be 12 km and v = 1 km/hr.

Time taken in 1st journey = Distance/Speed = 12/v = 12/1 = 12 hrs

Time taken in 2nd journey = 12/2v = 12/2 = 6 hrs

Time taken in 3rd Journey = 12/3v = 12/3 = 4 hrs

Time taken in 4th Journey = 12/4v = 12/4 = 3 hrs

Now, total distance = 12 × 4 = 48 kms

Average Speed = Total Distance/Total Time = 48 / (12 + 6 + 4 + 3) = 48/25 (this value lies between 1 and 2)

So, the average speed of the car for the entire journey lies between v and 2v.

व्याख्या Please wait..

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