AAA Express train travels 670 km in 6 hours and WWW Express train travels 950 km in 9 hours. What is the average speed of AAA and WWW Express trains?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 108 km/hr
The average speed of the two trains taken together is the total distance divided by the total time.
Total distance \(=670+950=1620\) km
Total time \(=6+9=15\) hours
Average speed \(\displaystyle =\frac{1620}{15}=108\) km/hr
Tip: The two speeds are about 111.7 km/hr and 105.6 km/hr, and their plain mean is about 108.6 km/hr. Averaging the speeds is not the same as the average speed when the times differ; the train that runs longer counts for more.