ISEE Upper Level Math : How to find the surface area of a cylinder

Study concepts, example questions & explanations for ISEE Upper Level Math

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Example Questions

Example Question #121 : Solid Geometry

If a cylinder has a height of 6 mm and a radius of 12 mm, what is its surface area?

 

Possible Answers:

\(\displaystyle 432 \pi mm^2\)

\(\displaystyle 144 \pi mm^2\)

\(\displaystyle 432 mm\)

\(\displaystyle 288 \pi mm^2\)

Correct answer:

\(\displaystyle 432 \pi mm^2\)

Explanation:

If a cylinder has a height of 6 mm and a radius of 12 mm, what is its surface area?

Find surface area with the following formula:

\(\displaystyle A=2\pi r h +2\pi r^2\)

This works because we are adding the area of the two bases to the area of the side.

Plug in and simplify:

\(\displaystyle A=2\pi (12mm)(6mm) +2\pi (12mm)^2=144\pi mm^2+288\pi mm^2=432 \pi mm^2\)

Example Question #121 : Solid Geometry

Find the volume of a cylinder with a diameter of 14cm and a height of 8cm.

Possible Answers:

\(\displaystyle 392\pi \text{ cm}^3\)

\(\displaystyle 56\pi \text{ cm}^3\)

\(\displaystyle 112\pi \text{ cm}^3\)

\(\displaystyle 896\pi \text{ cm}^3\)

\(\displaystyle 976\pi \text{ cm}^3\)

Correct answer:

\(\displaystyle 392\pi \text{ cm}^3\)

Explanation:

To find the volume of a cylinder, we will use the following formula:

\(\displaystyle V = \pi r^2 h\)

where r is the radius and h is the height of the cylinder. 

 

Now, we know the diameter of the cylinder is 14cm.  We also know that the diameter is two times the radius.  Therefore, the radius is 7cm.

We know the height of the cylinder is 8cm.

Knowing all of this, we can substitute into the formula.  We get

\(\displaystyle V = \pi \cdot (7\text{cm})^2 \cdot 8\text{cm}\)

\(\displaystyle V = \pi \cdot 49\text{cm}^2 \cdot 8\text{cm}\)

\(\displaystyle V = \pi \cdot 392\text{cm}^3\)

\(\displaystyle V = 392\pi \text{ cm}^3\)

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