Sonia travels to IBA from Uttara by car at a speed of 40 km per hour and returns to Uttara at a speed of 30 km per hour by an auto rickshaw. What is her average speed in the entire journey in km/hour?
A. 35
B. 34.3
C. 37.5
D. 35.3
E. 36
Explanation: Average speed \(= \frac{2uv}{u+v}\). Here \(u=40 \text{ kmph}\) and \(v=30 \text{ kmph}\). Average speed \(= \frac{2\times40\times30}{40+30} = \frac{2400}{70} \approx 34.3 \text{ kmph}\).
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