2. About 78 1cm?

3、 1200

4、20

5、5/ 17 2/9

6, 74.8 70.2 (the number of this question may be wrong. If the total is 155, the correct answer is: 80 75)

7、5 14

2. 1. Assuming that this barrel of gasoline has X kilograms, the equation can be expressed as: (30%x+30)×2+20=x, and the equation can be solved: X = 200 kilograms.

2. If it takes X days for Party B to finish it alone, the equation can be listed as follows:115× {10.5-(7/10)/(115+0/)

3. If it takes X days from start to finish, the equation can be listed as (x-2)/10+(x-8)/30 =1,and the equation can be solved as x =1/day.

4. It takes X hours for Team A to complete this work alone, and Y hours for Team B to complete this work alone, so the equation can be listed as follows: 4× (1/x+1/y) =1/48/y+20/x = 3/4.

By solving the equations, we can get: x=40 hours, y=20 hours.

5. If car A and car B travel at the speed of X km and Y km per hour respectively, the equation can be established: 3x/3y=5/4 (3x-3y)/2=36. By solving the equations, we can get: x = 120km y = 96km.

6、 1000×( 1-25%)= 750kg 750×( 1-40%)= 450kg 450×( 1-80%)= 90kg

7. Assuming that Party A and Party B originally had X yuan and Y yuan respectively, we can list the equations: x/y=7/3 y-20=5+0.2×(x+y) and solve the equations: x= 175 yuan y=75 yuan.

8. If there are X books and Y books on the original two floors, you can list the equation: x-y=20 (y-5)/(x+5)=4/7, and solve the equation: x=65 books and y=45 books.

There are too many, so I won't write.