Multiple choice

A boat goes upstream at a speed of 15 km/hr and comes back the same distance at 24 km/hr. What is the average speed (in km/hr) for the total journey? (Approx) एक नाव एक स्थान पर 15 किमी /घंटा की चाल से उर्ध्वप्रवाह जाती है और 24 किमी/घंटा की अनुप्रवाह चाल से वापस आती है। कुल यात्रा के दौरान औसत गति (किमी/घंटा में) क्या है? (लगभग)

  1. 17.4

  2. 18.5

  3. 19.3

  4. 18.9
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B Correct answer
Explanation

For equal distances at speeds 15 km/hr (upstream) and 24 km/hr (downstream), average speed = 2×15×24/(15+24) = 720/39 = 18.46 km/hr, approximately 18.5 km/hr. This is the harmonic mean of the two speeds.

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