Question 775914
3 people start with 4 days' food

Day 1, 3 people now have 3 days' food each, 1st person give a days' food to the other two, so 2 people have 4 days' food and the 1st has a days' food and heads home. 

Day 2, the 2 people each have 3 days' food, so one gives a day's food to the other. Now, the one with 2 Days' food heads home, and the one with 4 days' food has 4 days to get to the other side.