If a train travels from Onetown to Sometown at 60 mph and returns at 40 mph what is its average speed?
The average speed of the train for the entire trip would be the harmonic mean of 60 mph and 40 mph. Using the formula for harmonic mean: 2 * 60 * 40 / (60 + 40) = 48 mph. So, the average speed of the train is 48 mph.