Q109
ArithmeticSpeed, Time & Distance
If a man goes to a place at an average speed of 10 km/hr and then returns at the average speed of 15 km/hr. Find his average speed during the whole journey.
- a.12 km/hr
- b.12·5 km/hr
- c.13 km/hr
- d.15 km/hr
Answer: (A) 12 km/hr
For equal distances the average speed is $\frac{2xy}{x + y} = \frac{2 \times 10 \times 15}{25} = 12$ km/hr. 12·5 km/hr is the simple mean of the speeds, which is wrong because more time is spent at the slower speed.