I. 1, -3℃

2, 2 or -4

3, rational number subtraction rule A-B = A+(-B)

4, 2

5. The answer is not unique. For example, 0.5x= 1.5.

6. Fill in 0 and 5 in the second line and -0.5 in the third line.

7、 123

8、4

9.400 students' overall vision, the sample is 40 students' vision.

10、2.8

Second, 1 1, d; 12、B； 13、C； 14、D； 15、A； 16、A； 17、B； 18、C； 19、D； 20、D

Third, be careful.

1.( 1)-968; (2)y=- 1 .

2. Yuan ~ Yuan. (Note: The total length is (1 min) km;

The scheduled fare is calculated in RMB/km, and the fare is

The scheduled fare is calculated in RMB/km, and the fare is

That is, the fare range is yuan ~ yuan. )

3. Complementary angles of (1) and ∠AOD ∠BOD, ∠COD

The angles ∠AOE and ∠COE are complementary to ∠BOE.

(2)COD+∠COE =∠AOB = 90。

Tip: Because OD divides ∠BOC equally, ∠COD= ∠BOC.

And OE shares ∠AOC equally, so ∠COE= ∠AOC,

so∠COD+∠COE =∠BOC+∠AOC =∠BOC+∠AOC)，

So ∠ COD+∠ COE = ∠ AOB = 90.

4.( 1) ; 1,4,6,4, 1;

(2) , .

5.( 1) 1500m； (2)6825.6 yuan

6.( 1)400 meters

Tip: Suppose the distance between this city and a city is X kilometers.

According to the question, 200? + 15x+2000=200？ +20x+900- 1 100

Solving this equation gives x=400.

(2) When the total cost of trains and cars is the same, there are

.

Solve this equation and get s= 160.

That is, when the distance between this city and a city is greater than 160 km, it is more economical to choose train transportation;

When the distance between this city and a city is equal to 160 km, you can choose two modes of transportation: train and car.

When the distance between this city and a city is less than 160 km, it is more economical to choose car transportation.