The third grader went to the library to borrow books, borrowed 420 books in the morning, and borrowed 20 more books in the afternoon than in the morning. How many books are there in this third grade?
三年级去图书馆借书，上午借了420本，下午比上午多借20本．这一三年级共书多少本？
<gadget id="calculator">420 + 20 + 420</gadget>
<output>860</output>

<result>860</result>