Multiple choice

Four equal distance of 3 km are covered with the speed of 10 km/hr, 20km/hr, 30km/hr, and 60 km/hr respectively. Find the average speed of bus. एक बस द्वारा 3 किमी की 4 समान दूरियों को क्रमशः 10 किमी/घंटा, 20 किमी/घंटा, 30 किमी/घंटा, 60 किमी/घंटा की चाल से तय किया जाता है। बस की औसत चाल ज्ञात कीजिए।

  1. 30 km/hr. किमी/घंटा

  2. 25 km/hr. किमी/घंटा

  3. 20 km/hr. किमी/घंटा

  4. 10 km/hr. किमी/घंटा
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C Correct answer
Explanation

For equal distances, average speed = harmonic mean = 4/((1/10)+(1/20)+(1/30)+(1/60)). Simplifying: 4/((6+3+2+1)/60)=4/(12/60)=4×(60/12)=20 km/h. This is because at equal distances, more time is spent at lower speeds.

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