2. The car traveled half of the distance at a speed of 60 km/h, then one third of the remaining distance at a speed of 120 km/h, and the remaining distance at a speed of 80 km/h.

Find the average speed of the car during this trip. Give your answer in km/h.
Solution: Let x hours be the time the car traveled at a speed of 60 km/h, then $60 x=\frac{s}{2}$. Let y hours be the time the car traveled at a speed of 120 km/h, then $120 y=\frac{s}{6}$. Let z hours be the time the car traveled at a speed of 80 km/h, then $80 z=\frac{s}{3}$. By definition $v_{cp}=\frac{s}{t_{\text{total}}}$. Then $v_{cp}=\frac{s}{x+y+z}=\frac{s}{\frac{s}{120}+\frac{s}{720}+\frac{s}{240}}=\frac{1}{\frac{1}{120}+\frac{1}{6 \cdot 120}+\frac{1}{2 \cdot 120}}=\frac{6 \cdot 120}{10}=72$.

Answer: 72.