A man goes to a place in the car at speed of 160 km/h and comes back at a lower speed. If the average speed is 64 km/h in total, then the return speed (in km/h) is:

Let's assume the distance of one side is 'd'.

Let's assume the speed of the car in return time is 'b'.

A man goes to a place in the car at speed of 160 km/h and comes back at a lower speed. If the average speed is 64 km/h.

$$64 = \frac{d+d}{\frac{d}{160}+\frac{d}{ b}}$$

$$64=\frac{2d}{\frac{db+d160}{160b}}$$

$$64=\frac{2}{\frac{b+160}{160b}}$$

$$64=\frac{320b}{b+160}$$

$$1=\frac{5b}{b+160}$$

5b = b+160

5b-b = 160

4b = 160

speed of the car in return time = b = 40 km/h