Multiple choice

A man goes uphill with an average speed of 24 km/hr and comes down with an average speed of 36 km/hr. If the distance travelled in both the cases is the same, then find the average speed for the entire journey.

  1. 30 km/hr

  2. 24 km/hr

  3. 28.8 km/hr

  4. 32.6 km/hr

  5. 36 km/hr
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C Correct answer
Explanation

The average speed for a round trip with speeds v1 and v2 over the same distance is (2 * v1 * v2) / (v1 + v2). Plugging in 24 and 36: (2 * 24 * 36) / (24 + 36) = 1728 / 60 = 28.8 km/hr.

AI explanation

For a journey where equal distances are travelled at two different speeds, the formula for average speed is (2 multiplied by speed1 multiplied by speed2) divided by (speed1 + speed2). Substituting the uphill and downhill speeds gives (2 multiplied by 24 multiplied by 36) divided by (24 + 36). Solving the numerator and denominator gives 1728 divided by 60, which results in an average speed of 28.8 km/hr for the entire journey.

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