If the circumference of a circle is increased by 10%, how much will the area of the circle increase?
把一个圆的周长增加10%，则这个圆的面积增加多少．
<gadget id="calculator">21 / 100</gadget>
<output>21/100 = around 0.21</output>

<result>21/100 = around 0.21</result>