There is a three-story bookshelf, take 10 books from the first floor to the second floor, then take 15 books from the second floor to the first floor, and then take 20 books from the third floor and divide them equally between the first floor and the second floor. The second floor, so that the number of books on the third shelf is equal. Which floor has the most books? Which layer is the least? How much more is the most than the least?
有一个三层的书架，从第一层拿10本书到第二层，再从第二层拿15本书到第一层，然后从第三层拿20本平均分在第一层和第二层，这样三层书架上书的本数相等．原来哪一层上书的本数最多？哪一层最少？最多的比最少的多多少本？
<gadget id="calculator">10 + 15 + 10</gadget>
<output>35</output>

<result>35</result>