71. The bus traveled three equal-length segments of the route: the first at an average speed of 50 km/h, the second at 30 km/h, and the third at 70 km/h. What is the average speed of the bus over the entire route?
71. Let the length of one segment be $a$ km, then the bus spent $\left(\frac{a}{50}+\frac{a}{30}+\frac{a}{70}\right)$ hours to travel the entire path of length $3 a$ km. Therefore, the average speed of movement is

$$
3 a:\left(\frac{a}{50}+\frac{a}{30}+\frac{a}{70}\right)=\frac{3 \cdot 1050}{21+35+15} \approx 44(\text { km } / \mathrm{h}) .
$$