A car travels from A to B at a speed of 40 km/hr, travels back from B to A at a speed of 30 km/hr and again goes from A to B at a speed of 60 km/hr. What is the average speed of the car?
- A. \frac{130}{3} km/hr
- B. 42 km/hr
- C. 40 km/hr ✓
- D. \frac{125}{3} km/hr
Correct Answer: C. 40 km/hr
Explanation
For three equal distances, average speed is \frac{3}{\frac{1}{v_1}+\frac{1}{v_2}+\frac{1}{v_3}} = \frac{3}{\frac{1}{40}+\frac{1}{30}+\frac{1}{60}} = \frac{3}{\frac{3+4+2}{120}} = \frac{3}{\frac{9}{120}} = \frac{360}{9} = 40 km/hr.
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