Multiple choice

A car travels 30 km at a uniform speed of 40 km/h and the next 30 km at a uniform speed of 20 km/h. Find its average speed.

  1. 35 km/h

  2. 40 km/h

  3. 22 km/h

  4. 26.6 km/h
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D Correct answer
Explanation

Average speed = Total Distance / Total Time. Total distance = 30 + 30 = 60 km. Time 1 = 30/40 = 0.75 hours. Time 2 = 30/20 = 1.5 hours. Total time = 2.25 hours. Average speed = 60 / 2.25 = 26.66 km/h.

AI explanation

When equal distances are traveled at two different speeds, use the harmonic mean formula for average speed: 2xy divided by (x plus y). The time for the first 30 km is 30 divided by 40, which is 0.75 hours, and the time for the next 30 km is 30 divided by 20, which is 1.5 hours. The total distance is 60 km and the total time is 2.25 hours, so the average speed is 60 divided by 2.25, which gives 26.6 km/h.

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