The school library bought 1500 books on literature and art, of which 36 books were twice as few as those on science and technology. How many books are there?

Solution: If there are X scientific books, there are 2X-36 literary books. ..

X+2X-36= 1500

3X-36= 1500

3X= 1536

X=5 12

There are 2×5 12-36=988 literary and artistic books.

General solution of binary linear equation with extended data;

Elimination method: the unknowns in the equation are solved one by one from more to less.

There are two ways to eliminate elements:

1, instead of eliminating

Example: Solve the system of equations x+y = 5 16x+ 13y = 89②.

Solution: Take ③ from ① with x=5-y③ to ② to get 6(5-y)+ 13y=89 and y=59/7.

Bring y=59/7 into ③ to get x=5-59/7, that is, x=-24/7.

∴x=-24/7,y=59/7

This solution is the substitution elimination method.

2. Add, subtract and eliminate elements

Example: Solve the system of equations x+y=9① x-y=5②.

Solution: ①+②, 2x= 14, that is, x=7.

Bring x=7 into ① to get 7+y=9 and y=2.

∴x=7,y=2

This solution is addition, subtraction and elimination.