A new four-story teaching building has been built in a middle school. There are 8 classrooms on each floor, and there are 4 doors in and out of the building, of which 2 main doors are the same size and 2 side doors are the same size. For safety inspection, four doors were tested: when a main entrance and two side doors were opened at the same time, 560 students could pass in 2 minutes; When a main entrance and a side door are opened at the same time, 800 students can pass in 4 minutes.

1. Find the average number of students who can pass through a main entrance and a side door every minute;

2. During the inspection, it was found that the efficiency of going out was reduced by 20% due to the crowded students in an emergency. According to the safety inspection regulations, in case of emergency, students in the whole building should be evacuated safely through these four doors within 5 minutes. Suppose that each classroom in this teaching building has a maximum of 45 students. Q: Do these four doors meet the safety requirements? Please provide a justification for the answer.

: (1) Let an average of X students pass through a main entrance every minute.

Because when a main entrance and a side door are opened at the same time, 800 students can pass in 4 minutes.

Therefore, when a main entrance and a side door are opened at the same time, 1 minute can pass 200 students.

A main entrance can pass X students per minute on average, so a side door can pass 200-X students per minute on average.

Open a main entrance and two side doors at the same time, and 560 students can pass in 2 minutes.

So it can be listed as follows:

2*[x+2(200-x)]=560

X+400-2x=280。

The solution is x= 120.

So on average 120 and 80 students can pass through a main entrance and a side door every minute.

(2) Assuming that each classroom in the teaching building has at most 45 students,

Because the teaching building has four floors and each floor has eight classrooms, it can be seen that:

The teaching building can accommodate up to 4 * 8 * 45 = 1440 students.

In an emergency, the efficiency of going out is reduced by 20%, which means:

At this time, a main entrance can pass 120*( 1-20%)=96 students per minute on average; And a side door can pass 80( 1-20%)=80 students per minute on average.

According to the regulations, students in the whole building should be evacuated safely through these four doors within five minutes, so the number of students who can be evacuated safely through these four doors within five minutes is 5*2*(96+80)= 1760.

Obviously, due to 1760 >: 1440, it can be seen that these four doors meet the safety regulations!

A physical examination center has five scales: A, B, C, D and E. Due to long-term use, some scales are not accurate. Weighing the same person, their differences are as follows: C is 0.3kgd lighter than B and 0.1kg lighter than C; E is 0.1kg lighter than a; C is 0. 1kg lighter than E. Coincidentally, the average weight of five scales is the accurate weight. Now we know that only one scale is accurate. Please think about it. The exact weighing scale is ().

(A)A (B)B (C)D (D)E

List relation-suppose C=x, then b = x+0.3d = x-0.1e = a-0.1; e = x+0. 1->； A = x+0.2a+b+c+d+e = 5x+0.5 = 5 (x+0.1) = 5e (choose d! ) 8. Find the rule 0-10798 61-9687102-8107693-7961084-6810975 through finite enumeration. 9. The analysis shows that the given graph 1 12 has three complete edges, six residual edges and three missing edges (vertical A, flat B and oblique C). There are four real angles and four imaginary angles; Up, down, left, right, front, back, left, right, left, the single corner at the bottom is divided into four 2×2×4 column areas: front, left and right. The candidate diagram for full analysis of back column excludes the area of B-2x4x4 column that is not full. There are two separate horns. A- Visually, the 90 vertical axis rotation of the right hand is 180, and the vertical edges are not complementary. D- Visually, the 90 vertical axis rotation of the right hand is 180, while) it is 10. Analyze the law, don't be afraid of trouble! 10 -90 points1160 points * points +70 means 90+70 12 -250 points * points +90 points or more +20 means (90+70)+ 2+20)+(70+20 * 2) = 90+70 * 3+20 * 3 = 90+70 * 3+20 * (1+2)14-490 * 130 again. ... =' class1' > n-90+70 (n-10)+20 [1+2+...+(n-1)]} that is, 90+70 (n-/kloc-0). 10) to solve 90+70 (n-10)+20 (n-1) (n-10) =1000, that is, n 2. )