The length of a rectangle is 20 decimeters and the width is 10 decimeters. The perimeter of a square is equal to this rectangle. What is the side length of a square?
一个长方形长是20分米，宽是10分米，一个正方形的周长和这个长方形相等，一个正方形的边长是多少分米．
<gadget id="calculator">20 + 10</gadget>
<output>30</output>

<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">30 * (1/2)</gadget>
<output>15</output>

<result>15</result>