Answer
The answer is below.
Work Step by Step
a) When it moves this speed for half the total time, its average speed is the average of the velocities. Thus:
$v = \frac{v_1+v_2}{2}$
b) We know that half the total distance equals $\frac{L}{2}$. Thus, we find:
$v=\frac{L/2+L/2}{\frac{L/2}{v_1}+\frac{L/2}{v_2}}$
Thus, we find:
$v= \frac{2v_1v_2}{v_1+v_2}$
c) The average speed is greater in case a).
