If the outer and inner diameters of a ring are both 5 cm, what is the area of the ring in square centimetres?
一个圆环的外圆半径和内圆直径都是5cm，这个圆环的面积是多少平方厘米．
<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<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">25 - (25/4)</gadget>
<output>75/4 = around 18.75</output>

<gadget id="calculator">3.14 * (75/4)</gadget>
<output>58.875</output>

<result>58.875</result>