A car travels from point X to point Y. It travels at 30 km/h up to halfway and at 20 km/h for the rest of the journey. What is the car's average speed?
The answer seemed pretty simple at first, I mean, it's got to be 25 km/h. Since the car travels the same distance for each of the different speeds, shouldn't the distance really be negatable? Couldn't you just say the car's traveling at 20km/h at point A and 30km/h at point B, and so the average of the speeds should be 25km/h?
And yet, if you try applying an actual number to the distances, things change. Say the distance is 120km overall. This would mean that it would take 60/30 = 2h to cover the first half, and 60/20 = 3h to cover the second half. Seeing as distance is speed over time, the average speed would hence be 120/(2+3) = 120/5 = 24km/h.
How can this be possible? Can someone help me out here?