A nomad is injured in the desert. And he can't move, but fortunately an oasis is nearby, and he can stay there for enough time until rescue arrives. But the water is a magical water, that it can't be stored. So it should be drunk immediately or it'll disappear. In other words, one cannot bring the water outside the oasis.
The other nomad friends, know the exact position of the injured nomad, which is $n$ days away from the base. The nomads are going to send delegations to save him, but the problem is that each nomad can only bring food supply for one nomad for $3$ days. The base has arbitrarily large number of nomads inside, so they decided to send a group of nomads to rescue the injured nomad, that is, to go to the place of injured nomad, and then go back to the base. All nomads must survive. But they have weird cultural rules, which is each time a nomad leaves the base, they have to kill a sheep as redemption.
Note that the injured nomad also need to eat while going back to the base.
What is the number of sheep need to be slaughtered in order to save the injured nomad in case n=2? n=3? arbitrary n?
Furthermore, what is the minimum number of days required to save the nomad?
For example, if n=1, the nomad group can just send one nomad. It'll consume 1 day of supply, then arrives at the injured nomad place with 2 days of supply left, then each of them consume 1 day of supply while going back to the base, leaving no supply left when they arrived at the base. Since only one nomad leaves the base, only one sheep is killed. So 1 sheep will be slaughtered, and the rescue time is 2 days.
- This is generalisation to Travellers across a desert with a twist that everybody should come back to the base