There is a square log whose cross-section is square and whose side length is 4 decimeters, which is equivalent to (1/10) the total length of the square log. Now process this square log into the largest cylinder. Find the loss rate of this piece of wood.
有一块方木，其横截面为正方形，边长为4分米，相当于方木全长的(1/10)．现在把这块方木加工成一个最大的圆柱．求这块木料的损耗率．
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">4 / (1/10)</gadget>
<output>40</output>

<gadget id="calculator">4 * 4 * 40</gadget>
<output>640</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">3.14 * 4 * 40</gadget>
<output>502.4</output>

<gadget id="calculator">640 - 502.4</gadget>
<output>137.6</output>

<gadget id="calculator">137.6 / 640</gadget>
<output>0.215</output>

<result>0.215</result>