A vehicle travels 50% of its distance at 2 km/h, and the remaining 50% at 8 km/h. What is the total distance, if it travelled for a total duration of 20 hours?
Let 2x be the actual duration of the journey. Then, $x/2 + x/8 = 20$. Solving for x we get x = 32, and so, 2x = 64 km.