The diameter of the bottom of a cylinder is 4 decimeters, and the height is 5 decimeters. If it is cut in half along the diameter, how many square decimeters will the surface area increase?
一个圆柱体底面的直径是4分米，高是5分米，如果把它沿直径劈成两半，表面积增加了多少平方分米？
<gadget id="calculator">5 * 4 * 2</gadget>
<output>40</output>

<result>40</result>