The total score of five students is 90*5=450, and the higher the score of the first and second students, the better (100,99). The lowest total score of the third and fourth students is

450- 100-99-75= 176

176/2=88

So the third place and the fourth place are 89 and 87 respectively.

2,

It takes 8+12+14+17+18+23+30 =122 minutes for seven students to make up in turn. Now three people are working at the same time, and the average share of each person is 122/3, which is about 4 1 minute. Three teachers drew lots for seven people. Observing the characteristics of these times, we will know that two of them draw two people and the other draws three people. The longest time 30 can only match 12 minutes, the closest time is 4 1, 30+ 12=42 minutes, and so on, 23 and 17 match exactly 40 minutes, and the remaining 8+14+/. So it takes at least 42 minutes to complete the makeup task.

three

It takes 4+5+6+6+8+9+9=47 minutes to water seven seedlings at a time, with an average share of 47/3, which is about 15.6 minutes. Three people and seven trees means that one person waters three trees and the other two people waters two trees. The shorter the time for watering three trees, the better. The longer the time for watering two trees, the better.

The following combinations are the most

4+5+6= 15; 9+6= 15; 9+8= 17

4+6+6= 16; 9+5= 14; 9+8= 17

4+5+8= 17; 9+6= 15; 9+6= 15

So it takes at least 17 minutes to finish all the watering.