Answer
45.3 is the harmonic mean, which represents the mean speed of the trip.
Work Step by Step
The mean speed is (38+56)/2=47, but the harmonic mean of speed is: $\frac{2}{\frac{1}{38}+\frac{1}{56}}=45.3$, and this is actually the mean speed of the trip because $time=\frac{distance}{speed}$.
