The explorer Sir Randolph Fiend set out to cross the Little Red Desert alone on foot.
The length of the crossing is 150 km and Fiend could cover 30 km a day.
Food and water were available on the other side but he could carry no more than three days' rations.
Nevertheless, after some careful planning Fiend managed to make the crossing - in the shortest time possible in the circumstances.

How long did he take?

The answer is supposed to be 11.8 days and I have a worked solution by a maths professor from James Cook University and I still can't see it!
And even he couldn't prove this answer is a minimum!

Good Luck!