AMC10 2004 A

AMC10 2004 A · Q19

AMC10 2004 A · Q19. It mainly tests 3D geometry (surface area).

A white cylindrical silo has a diameter of 30 feet and a height of 80 feet. A red stripe with a horizontal width of 3 feet is painted on the silo, as shown, making two complete revolutions around it. What is the area of the stripe in square feet?

一个白色圆柱形筒仓直径为 30 英尺，高为 80 英尺。如图所示，筒仓上画有一条水平宽度为 3 英尺的红色条纹，绕筒仓绕了两整圈。条纹的面积是多少平方英尺？

(A) 120 120

(B) 180 180

(D) 360 360

(E) 480 480

Answer

Correct choice: (C)

正确答案：（C）

Solution

If the stripe were cut from the silo and spread flat, it would form a parallelogram 3 feet wide and 80 feet high. So the area of the stripe is $3(80) = 240$ square feet.

如果将条纹从筒仓上剪下并展开平铺，它将形成一个宽 3 英尺、高 80 英尺的平行四边形。因此条纹面积为 $3(80) = 240$ 平方英尺。

Topics

GE.014 3D geometry (surface area)