Cut a rectangular board with a length of 8 cm and a width of 5 cm into the largest circular board. What is the area in square centimeters after cutting off the leftovers?
把一块长是8cm，宽是5cm的长方形木板，剪成一个最大的圆形木板，剪去边角料的面积是多平方厘米？
<gadget id="calculator">8 * 5</gadget>
<output>40</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">(5/2) ** 2</gadget>
<output>25/4 = around 6.25</output>

<gadget id="calculator">3.14 * (25/4)</gadget>
<output>19.625</output>

<gadget id="calculator">40 - 19.625</gadget>
<output>20.375</output>

<result>20.375</result>