If the circumference of a circle is reduced by 10%, how much will the area be reduced?
一个圆，周长减少10%，面积将减少多少．
<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 - (1/10)</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">(9/10) * (9/10)</gadget>
<output>81/100 = around 0.81</output>

<gadget id="calculator">1 - (81/100)</gadget>
<output>19/100 = around 0.19</output>

<result>19/100 = around 0.19</result>