Divide the bottom surface of a cylinder with a height of 5 decimeters into several sectors, then cut the cylinder and put it together to form an approximate cuboid with the same base and height. The surface area of the cuboid is increased by 40 square centimeters. Find the volume of the original cylinder.
把一个高5分米的圆柱体底面平均分成若干扇形，然后把圆柱体切开，拼成一个与它等底等高的近似长方体，长方体的表面积增加40平方厘米，求原来圆柱体的体积．
<gadget id="calculator">40 / 2 / 5</gadget>
<output>4</output>

<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">3.14 * 16 * 5</gadget>
<output>251.2</output>

<result>251.2</result>