Multiple choice

A car moves at $80$ km/hr in the first half of total time of motion and at $40$ km$/h^{-1}$ in the later half. Its average speed is?

  1. $60$ km/hr
  2. $30$ km/hr
  3. $120$ km/hr

  4. None of these
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A Correct answer
Explanation

Average speed = Total distance / Total time. Let total time be 2T. First half time T, speed 80, distance 80T. Second half time T, speed 40, distance 40T. Total distance = 120T. Average speed = 120T / 2T = 60 km/hr.

AI explanation

When a journey is divided into equal intervals of time, the average speed equals the arithmetic mean of the speeds. Using this principle, we calculate (80 + 40) / 2. The average speed is 60 km/hr.

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