Three people should bring as much food as possible. First, divide the second person's food into five parts, and the first person gets 1 part, and the other two people get two parts respectively. Let's leave now. After 8/5 days, the second person returned, and the third person also had enough food to return; At this time, the third person's food is divided into three parts on average, 1 person gets 1 part, and the third person gets 2 parts, and moves on; After another 8/3 days, the third person came back, and at this time the third person still had enough food to come back; Finally, 1 people can walk on their own food for 8 days. 8+8÷3+8÷5≈ 12.3 (days), two assistants helped the explorer cross the desert.

Self-sequence11+1/3+1/5+1/7+1/9+1+0/... It seems!

But, but! Math expert, I remind you: If the time to cross the desert exceeds 16 days, some assistants will not have to go back the same way. Let's cross the desert with the explorers, and you can save some assistants! However, this is not your problem.

Ask again after a reward of 50 points, and listen to the next explanation.