Question

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?

$120$

$180$

$240$

$360$

$480$

Answer: C

Concepts:cylinder net (3D geometry)parallelogram

Difficulty rating: 1600

Small Hint:

Imagine cutting the stripe from the silo and unrolling it flat

Big Hint:

It becomes a parallelogram with horizontal width $3$ and height $80$

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.

2004 AMC 10A Problem 19

Answer: C

Difficulty rating: 1600

Small Hint:

Big Hint:

Solution:

Problem 19 in Other Years