4.(22-2.5×4)÷4=3 (Ben) 7. Solution: Suppose Xiaoming is X years old this year, then his mother is 3x years old.

From the meaning of the question, 3x-x=24 is an equation, and the equation is 2x=24.

Solution: suppose there are x books in the inventor series. x= 12

From the meaning of the title, 2.5×4+4x=22, so 3x=3× 12=36 (years old).

10+4x=22 A: Xiaoming 12 years old, mother is 36 years old.

4x= 12

x=3

A: There are three series of inventors.

Although it has been more than 30 minutes, I hope to adopt it because of hard work ~ ~