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 ~ ~