There are 6 different books and 7 different movies in the ' crazy silly school ' series. If you read 33 of the movies and watched 8 of the books How many more movies than books have you read?
There are a total of 13 different books and movies in the series. 
You have read 33 of the movies and 8 of the books. 
That means you have read 20 more movies than books.