Cut a 4-meter-long cylindrical log into 5 small logs, and the surface area increases by 8 square decimeters. What is the original volume of the log?
把一根长4米的圆柱木料截成5段小圆木，表面积增加8平方分米，这根圆木原来的体积是多少立方分米．
<gadget id="calculator">8 / 8</gadget>
<output>1</output>

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

<result>40</result>