Question

从一张 $20$ 单位乘 $30$ 单位的长方形硬纸板上切去四个边长为 $5$ 单位的角正方形，然后把四边折起形成一个无盖盒子。盒子内部表面积是多少平方单位？

Square corners, $5$ units on a side, are removed from a $20$ unit by $30$ unit rectangular sheet of cardboard. The sides are then folded to form an open box. The surface area, in square units, of the interior of the box is

$300$

$500$

$550$

$600$

$1000$

答案：B

知识点：表面积展开图（立体几何）

难度评级：980

解答：

盒子内部表面正好是切去四角后纸板的一面。原纸板面积为 $20 \times 30 = 600$ ，每个被切去的角面积为 $5 \times 5 = 25$ 。

所以内部表面积是 $600 - 4 \times 25 = 500$ 。

所以正确答案是 B。

The interior surface is exactly one face of the cardboard after the corners are removed. The sheet has area $20 \times 30 = 600,$ and each removed corner has area $5 \times 5 = 25.$

So the interior surface area is $600 - 4 \times 25 = 500.$

Thus, the correct answer is B .

1993 AMC 8 第 17 题

答案：B

难度评级：980

解答：

其他年份的第 17 题