There are some books in the school book corner. After borrowing (3/5), 20 new books are added. At this time, the number of remaining books is exactly the original (1/2). How many books are there in the book corner?
学校图书角有一些书，借走(3/5)后，又新增加20册，这时剩下图书的册数正好是原来的(1/2)．图书角原来有图书多少册？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(1/2) - (2/5)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">20 / (1/10)</gadget>
<output>200</output>

<result>200</result>