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Question
(The image features a close-up shot of a pen. The pen measures 22 cm in length and has a diameter of 3 cm. The numbers indicating the dimensions are positioned nearby, emphasizing the pen's elongated shape. The overall appearance showcases the sleek design and intricate details of the pen, inviting viewers to appreciate its craftsmanship. Tags related to text and bag suggest potential uses for this pen in writing or organization contexts.)

Krubell wants to make a new pencil case for the upcoming school year. He will use a circular cylinder template with a radius of 3 cm
and a height of 22 cm
.

How much fabric will Krubell need to make his pencil case? Use π = 3.14
.

Responses
A
414 point 4 8 cm squared
B
442 point 7 4 cm squared
C
471 cm squared
D
621.72 cm 2

1 answer

To find the amount of fabric Krubell will need to make the pencil case in the shape of a circular cylinder, we need to calculate the surface area of the cylinder.

The surface area \( A \) of a cylinder is given by the formula:

\[ A = 2\pi rh + 2\pi r^2 \]

Where:

  • \( r \) is the radius of the cylinder
  • \( h \) is the height of the cylinder

In this case, we have:

  • Radius \( r = 3 \) cm
  • Height \( h = 22 \) cm
  • Using \( \pi = 3.14 \)

Now, let's calculate the surface area step by step.

Step 1: Calculate the lateral surface area

The lateral surface area (the curved surface area) is given by:

\[ A_{\text{lateral}} = 2\pi rh = 2 \times 3.14 \times 3 \times 22 \]

Calculating this:

\[ A_{\text{lateral}} = 2 \times 3.14 \times 3 \times 22 = 2 \times 3.14 \times 66 = 2 \times 207.24 = 414.48 \text{ cm}^2 \]

Step 2: Calculate the area of the two circular bases

The area of one circular base is given by:

\[ A_{\text{base}} = \pi r^2 = 3.14 \times (3)^2 = 3.14 \times 9 = 28.26 \text{ cm}^2 \]

Since there are two bases:

\[ A_{\text{bases}} = 2 \times A_{\text{base}} = 2 \times 28.26 = 56.52 \text{ cm}^2 \]

Step 3: Calculate the total surface area

Now add the lateral surface area and the area of the bases:

\[ A = A_{\text{lateral}} + A_{\text{bases}} = 414.48 + 56.52 = 471 \text{ cm}^2 \]

Thus, the total amount of fabric Krubell will need to make the pencil case is:

\[ \boxed{471 \text{ cm}^2} \]

This matches option C: C. 471 cm²