Let the total number of books be \(10u\) (hardcover \(3u\), paperback \(7u\)).<br><br>
&bull; Hardcover fiction = \(\frac{2}{2+1} \times 3u = \frac{2}{3} \times 3u = 2u\).<br>
&bull; Hardcover non-fiction = \(\frac{1}{3} \times 3u = 1u\).<br>
&bull; Paperback fiction = \(\frac{4}{4+3} \times 7u = \frac{4}{7} \times 7u = 4u\).<br>
&bull; Paperback non-fiction = \(\frac{3}{7} \times 7u = 3u\).<br>
&bull; Total fiction = \(2u + 4u = 6u\); total non-fiction = \(1u + 3u = 4u\).<br>
&bull; Ratio = \(6u : 4u = 3 : 2\).<br><br>
Final Answer: 3 : 2