Divide a circle into several equal parts and put together an approximate rectangle. The perimeter of the rectangle is 40 decimeters longer than the perimeter of the circle. What is the perimeter of the circle in decimeters?
把一个圆分成若干等份，拼成一个近似的长方形，长方形的周长比圆的周长多40分米，圆的周长是多少分米．
<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">3.14 * 20 * 2</gadget>
<output>125.6</output>

<result>125.6</result>