Jerry had 8 action figures and 9 books on a shelf in his room. Later he added 10 more books to the shelf. How many books were on his shelf in all?
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Jerry had 8 action figures and 9 books on a shelf in his room. 

This means that there were a total of 8 + 9 = 17 items on the shelf. 

Later, he added 10 more books to the shelf. 

This means that there are now a total of 17 + 10 = 27 items on the shelf. 

Of those 27 items, the number of books is: 

9 + 10 = 19.