The number of library books in a school increased by 20% after it bought new books in may. The number increased by another 20% after a bookstore donated 300 books in June. Find the number of books in the library before it bought new books in May.

To find the number of books in the library before it bought new books in May, we can work backwards using percentages.

Let's assume the number of books before it bought new books in May is x.

After the school bought new books in May, the number of books increased by 20%. This means the new number of books in the library became x + 0.20x or 1.20x.

After the bookstore donated 300 books in June, the number of books increased by another 20%. This means the new number of books became 1.20x + 0.20(1.20x).

Simplifying the expression, we have:

1.20x + 0.20(1.20x) = x + 300

1.20x + 0.24x = x + 300

1.44x = x + 300

0.44x = 300

x = 300 / 0.44

x ≈ 681.82

Therefore, the number of books in the library before it bought new books in May was approximately 681.82.