The length of a piece of rectangular paper is 20 cm. Wang Xiaodong just draws a semicircle on this piece of paper. What is the area of the rectangular paper in square centimeters?
一张长方形纸的长是20厘米，王小东在这张纸上正好画一个半圆，长方形纸的面积是多少平方厘米．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">20 * 10</gadget>
<output>200</output>

<result>200</result>