Solution:

Suppose: 2 1 class donates X books, and class 22 donates Y books.

X-Y= 19

X+Y-Y=32

Then: x=32 Y= 13

Two classes donated 32+ 13=45 books.

Extended data

The concept and operation order of four operations

1, addition, subtraction, multiplication and division are called four operations.

2. In the formula without brackets, if there is only addition, subtraction or multiplication and division, it should be calculated from left to right.

3. If there are multiplication and division and addition and subtraction in the formula without brackets, calculate the multiplication and division first and then the addition and subtraction.

4. If there are brackets in the formula, count the inner side of brackets first, and then the outer side of brackets; The calculation order of large, medium and small brackets is small → medium → large. The calculation order in brackets follows the above calculation order of 1, 2 and 3.