A cylindrical piece of wood 5 meters long is sawn in half along its diameter to increase its surface area by 20 square decimeters. What is the diameter of this piece of wood.
将一根长5米的圆柱形木料沿着直径锯成相等的两半，表面积增加了20平方分米．这根木料的直径是多少．
<gadget id="calculator">20 / 2 / 5</gadget>
<output>2</output>

<result>2</result>