A person walks from his house to his office at a speed of $x_1$ km/hr and returns by the same route at a speed of $x_2$ km/hr. What is his average speed?

$\frac{x_1+x_2}{2}$ $\frac{x_1+x_2}{2x_1x_2}$ $\frac{2x_1x_2}{x_1+x_2}$ $\frac{x_1+x_2}{x_1x_2}$

$\frac{2x_1x_2}{x_1+x_2}$

The correct answer is Option (3) → $\frac{2x_1x_2}{x_1+x_2}$