The radius of a circle is r meters, and 8:r=r:(5/2), what is the area of this circle.
一个圆的半径r米，且8：r=r：(5/2)，这个圆的面积是多少．
<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">8 * (5/2)</gadget>
<output>20</output>

<gadget id="calculator">3.14 * 20</gadget>
<output>62.8</output>

<result>62.8</result>