Answer: David has 11 DVDs and 27 books.
Explanation:
When numbers are put in ratio form they are meant to compare their relative sizes.
The first number will be the first item being compared to the other.
For instance, if you had 2 pens and 3 pencils, the ratio of your pens to your pencils will be; 2:3. The ratio of your pencils to your pens however is 3:2.
In the same vein, a ratio of books to DVDs of 27:11 means that David has 27 books and 11 DVDs.