A person must carry a message through the desert. To cross it is necessary 9 days however, a person can bring food for 12 days only. There is no food in the place where the message should be left or in the desert.
Is it possible that between two people they are able to carry the message and return without missing food?
It is possible as follows:
The two people come out together TO Y B. The night from 3rd to 4th day, B gives to TO food for three days, so to TO He still has food for 12 days. The next day everyone takes a different path, TO keep on going until the message is delivered and B He turns around. The ninth day, TO will deliver the message still having food for 6 more days. The next day, TO undertakes the return and after two days B will leave from the starting point in search of TO With food for 12 days. They will meet just when they have 5 days left on their way back to TO. So B he will distribute half of his food to TO each having enough food to get home safe and sound.