Solution: let's assume that these students jump x times on average.

20X = 120 * 8+(X+ 10)* 12

The solution is X= 135 (below)

A: These students jump 135 times on average.

2. Solution:

Firstly, divide 2/3 and 5/ 12 into 8/ 12 and 5/ 12. Let the simplest fraction divide 2/3 and 5/ 12 by X/ 12. The same number added and subtracted by molecules is y.

The title means: (X+Y)/ 12=2/3.

(X-Y)/ 12=5/ 12

The solution is X= 13/2.

Y=3/2

So the original simplest score is X/ 12= 13/24.

A: The original simplest score was 13/24.

3. Solution:

The teacher's salary is x yuan, according to the meaning of the question:

(6000*5+X)/6+3000=X

The solution is X=9600 (yuan)

A: The master's salary is 9600 yuan.

I hope you are satisfied. If you need to solve the problem, you can make it up.