Multiple choice

A person covers a certain distance by car at a speed of 30 km/h and comes back at a speed of 40 km/h.The average speed during the travel is

  1. $34.3$ km/h
  2. $35$ km/h
  3. $37.5$ km/h
  4. $32.8$ km/h
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A Correct answer
Explanation

The average speed for a round trip with speeds v1 and v2 is given by the formula (2 * v1 * v2) / (v1 + v2). Plugging in 30 and 40 gives (2 * 30 * 40) / (30 + 40) = 2400 / 70 = 34.2857 km/h, which rounds to 34.3 km/h.

AI explanation

Since the person covers equal distances in both directions, we use the harmonic mean formula for average speed: 2ab divided by the sum of a and b. Substituting the given speeds, we calculate 2 multiplied by 30 multiplied by 40 divided by 30 plus 40, which equals 2400 divided by 70. This simplifies to 34.3 km/h. The average speed is 34.3 km/h.

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