A car drives downhill with the speed of 90 m/h. On a level road, the same car goes 72 m/h, and uphill it goes "only" 60 m/h.
It takes this car 5 hours to go from town A to town B. The return trip only takes 4 hours.
Find the distance between the two towns.
Great question! I just did it (without looking at the answers) and I liked it. But I do not think it deserves the difficulity 5 of 5 status. There are many approaches to this question, from pure algebra to logical thinking, and that makes it quite easy. I think it should be more a difficulity 3 of 5 question. (at least not higher)