Saw the largest semicircle from a rectangular board with a length of 10 decimeters and a width of 8 decimeters. How many square decimeters is the remaining board?
从一个长10分米，宽8分米的长方形木板上锯下一个最大的半圆，剩下的木板是多少平方分米？
<gadget id="calculator">10 * 8</gadget>
<output>80</output>

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">25 / 2</gadget>
<output>25/2 = around 12.5</output>

<gadget id="calculator">3.14 * (25/2)</gadget>
<output>39.25</output>

<gadget id="calculator">80 - 39.25</gadget>
<output>40.75</output>

<result>40.75</result>