The library of a school bought 140 new books, ending up with $\frac{27}{25}$ of the number of books it had before the purchase. The number of books before this purchase was:
(a) 1750;
(b) 2500;
(c) 2780;
(d) 2140;
(e) 1140.
When buying 140 books, the library ended up with $\frac{27}{25}$ of the number of books, therefore, 140 corresponds to $\frac{2}{25}$ of the books in the library. If $\frac{2}{25}$ corresponds to 140 books, $\frac{1}{25}$ corresponds to $140 \div 2=70$ books and $\frac{25}{25}$ to $70 \times 25=1750$ books. The correct option is (a).