A bus covers the first half of a certain distance with speed v1 and the second half with a speed v2. The average speed during the whole journey is:

उत्तर देखें और व्याख्या

उत्तर: (B) 2v1v2 / (v1 + v2)

व्याख्या

Average speed = total distance / total time = 2d / (d/v1 + d/v2) = 2v1v2/(v1 + v2), the harmonic mean.