There are two layers of books on the bookshelf. There are 50 books on the upper layer. Take out (1/5) from the upper layer and put them in the lower layer. Then the number of books on the upper and lower layers is the same. How many books are there in the lower layer?
书架上有两层书，上层有50本，拿出上层的(1/5)放入下层，则上、下两层的本数一样多，原来下层有多少本书？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) * 50</gadget>
<output>10</output>

<gadget id="calculator">50 * (1/5)</gadget>
<output>10</output>

<gadget id="calculator">50 - 10 - 10</gadget>
<output>30</output>

<result>30</result>