Help me solve some math application problems.

1, solution: assumption: originally divided into x groups.

8x= 12(x-2)

8x= 12x-24

4x=24

x=6

8×6=48

There are 48 students.

2. Solution: Let the decimal digit of this three-digit number be X, and the digit on the hundredth digit be x+ 1.

The unit is 3x-2, and the size of this three-digit number is100× (x+1)+10× x+(3x-2).

The size of the inverted three digits is100× (3x-2)+10× x+(x+1).

100×(x+ 1)+ 10×x+(3x-2)+ 100×(3x-2)+ 10×x+(x+ 1)= 1 17 1

100(4x- 1)+20x+(4x- 1)= 1 17 1

424 x- 10 1 = 1 17 1

424x= 1272

x=3

x+ 1=4 3x-2=7

A: This three-digit number is 437.

3. Solution: Suppose three classes * * * donated X books, then two classes donated x/3 books and three classes donated 40% X.

152+x/3+40%x=x

152=4/ 15x

x=570

A: Three classes donated 570 copies.

4. Solution: Suppose: the original price of each color TV is X yuan.

x( 1+40%)×80%-x = 2700÷ 10

1. 12x-x=270

0. 12x=270

x=2250

A: The original price of each color TV set is 2250 yuan.

5. Solution: Assume that the expressway distance between Party A and Party B is X kilometers and the hourly speed is x/4.

Speed × time = distance

(x/4-30)×7=x+30

7x-840=4x+ 120

3x=960

x=320

A: The expressway distance between A and B is 320 kilometers.