2004 AMC 10A 第 19 题

Question

一个白色圆柱形筒仓直径为

30

英尺，高为

80

英尺。如图，筒仓上涂了一条水平宽度为

3

英尺的红色条纹，绕筒仓完整转了两圈。条纹面积是多少平方英尺？

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?

120

180

240

360

480

想象把筒仓上的条纹剪下并展开成平面图形。

Imagine cutting the stripe from the silo and unrolling it flat

它会变成一个水平宽度为

3

、高为

80

的平行四边形。

It becomes a parallelogram with horizontal width

3

and height

80

将条纹展开后，它成为一个平行四边形。其底边（水平宽度）为

3

英尺，高跨过整个筒仓，为

80

英尺。

因此面积为

3 \times 80 = 240

平方英尺。

所以正确答案是 C。

Unrolling the stripe flattens it into a parallelogram. Its base (the horizontal width) is

3

feet and its height spans the full

80

feet of the silo.

The area is therefore

3 \times 80 = 240

square feet.

Thus, the correct answer is C.

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