(3950-3500)x5%=22.5 yuan.

24÷5%+3500=3980 (yuan)

A: Zhang Ming's father's monthly salary is 3,950 yuan, and he should pay personal income tax of 22.5 yuan.

If Liu Xing's father pays personal income tax in 24 yuan, his personal salary is 3,980 yuan, which is higher than that of Zhang Ming's father.

People's wages are higher than 30 yuan.

2. Solution:

3÷( 1÷8)×2-3

=3÷0. 125×2-3

=45 (person)

Answer: There are 45 students in Class 6 (1).

3. Solution:

1350 ÷ (1-90%) =1500 (yuan)

A: original fare 1500 yuan.

4. Solution:

19- 120%x=7

19- 1.2x=7

19-7= 1.2x

1.2x= 12

x= 10

5. Solution:

Let the total amount of money of A be X, then the total amount of money of B is:

X( 1-20%)=0.8X

It turns out that B has less money than A:

X-0.8X=0.2X

0.2X ÷X=20%

A: It turns out that B has less money than A (20%).