Question: A train travels from City X to City Y at a speed of 90 km/h and returns at a speed of 60 km/h. What is the average speed for the entire journey?
Options:
Correct Answer: 72 km/h
Solution:
Average speed = 2ab / (a + b) = 2 × 90 × 60 / (90 + 60) = 72 km/h.