Buy 30 books of three kinds, a total of 130 yuan. Among them, there are 5 yuan for science and technology books, 6 yuan for story books and 4 yuan for literature books. How many books did you buy each of these three books? Set up X science books and Y story books first, so there are 30-x-y literary books.

Get: 5x+6y+4*(30-x-y)= 130.

Simplification: x+2y= 10

Column equation, when the solution of variant X+2Y= 10 is discussed, Y is an integer greater than 0 and less than 5, and then four solutions are obtained by substituting variant Z-Y=20: (unit/book).

8, 1,2 1

6,2,22

4,3,23

2,4,24

Four ways, just write it down and it's ok! Hehe, O(∩_∩)O~ gives points.