A ring has an outer diameter of 5 decimeters and a width of 1 decimeter. What is the area of the ring?
一个圆环，外圆直径是5分米，圆环宽1分米，圆环的面积是多少．
<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">(5/2) ** 2</gadget>
<output>25/4 = around 6.25</output>

<gadget id="calculator">3.14 * (25/4)</gadget>
<output>19.625</output>

<gadget id="calculator">(5/2) - 1</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">(3/2) ** 2</gadget>
<output>9/4 = around 2.25</output>

<gadget id="calculator">3.14 * (9/4)</gadget>
<output>7.065</output>

<gadget id="calculator">19.625 - 7.065</gadget>
<output>12.56</output>

<result>12.56</result>