2004 AMC 10A Problem 19

Problem 19 of 25HarderGeometry

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?

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Solution

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.