For a ring, the radius of the inner circle is (1/3) of the radius of the outer circle, and the area of the inner circle is equal to the area of the ring.
一个圆环，内圆半径是外圆半径的(1/3)，这个内圆面积是圆环面积的多少．
<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

<result>1/8 = around 0.125</result>