A ring, the radius of the outer circle is 5dm, and the radius of the inner circle is 3dm, what is the area of the ring in dm**2.
一个环形，外圆的半径是5dm，内圆的半径是3dm，这个环形的面积是多少dm**2．
<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

<gadget id="calculator">25 - 9</gadget>
<output>16</output>

<gadget id="calculator">3.14 * 16</gadget>
<output>50.24</output>

<result>50.24</result>