GRE Math : Solid Geometry

Study concepts, example questions & explanations for GRE Math

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Example Questions

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Example Question #1 :How To Find The Surface Area Of A Cylinder

The area of the base of a circular right cylinder is quadrupled. By what percentage is the outer face increased by this change?

Possible Answers:

200%

100%

300%

250%

400%

Correct answer:

100%

Explanation:

The base of the original cylinder would have beenπr2, and the outer face would have been 2πrh, where h is the height of the cylinder.

Let's represent the original area with A, the original radius with r, and the new radius with R: therefore, we know πR2= 4A, or πR2=4πr2.Solving for R, we get R = 2r; therefore, the new outer face of the cylinder will have an area of 2πRh or 2π2rh or 4πrh, which is double the original face area; thus the percentage of increase is 100%. (Don't be tricked into thinking it is 200%. That is not the percentage ofincrease.)

Example Question #1 :How To Find The Surface Area Of A Cylinder

What is the surface area of a cylinder with a radius of 17 and a height of 3?

Possible Answers:

3107

1984

2137

2205

2000

Correct answer:

2137

Explanation:

We need the formula for the surface area of a cylinder: SA = 2πr2+ 2πrh. This formula hasπin it, but the answer choices don't. This means we must approximateπ. None of the answers are too close to each other so we could really even use 3 here, but it is safest to use 3.14 as an approximate value ofπ.

Then SA = 2 * 3.14 * 172+ 2 * 3.14 * 17 * 3 ≈ 2137

Example Question #1 :Solid Geometry

What is the surface area of a cylinder with a radius of 6 and a height of 9?

Possible Answers:

108π

180π

64π

225π

96π

Correct answer:

180π

Explanation:

surface area of a cylinder

= 2πr2+ 2πrh

= 2π* 62+ 2π* 6 *9

= 180π

Example Question #1 :How To Find The Surface Area Of A Cylinder

Quantitative Comparison

Quantity A: The volume of a cylinder with a radius of 3 and a height of 4

Quantity B: 3 times the volume of a cone with a radius of 3 and a height of 4

Possible Answers:

Quantity B is greater.

Quantity A is greater.

The two quantities are equal.

The relationship cannot be determined from the information given.

Correct answer:

The two quantities are equal.

Explanation:

There is no need to do the actual computations here to find the two volumes. The volume of a cone is exactly 1/3 the volume of a cylinder with the same height and radius. That means the two quantities are equal. The formulas show this relationship as well: volume of a cone =πr2h/3 and volume of a cylinder =πr2h.

Example Question #1 :Solid Geometry

A right circular cylinder of volumehas a height of 8.

Quantity A: 10

Quantity B: The circumference of the base

Possible Answers:

Quantity B is greater

The two quantities are equal

The relationship cannot be determined from the information provided.

Quantity A is greater

Correct answer:

Quantity B is greater

Explanation:

The volume of any solid figure is. In this case, the volume of the cylinder isand its height is, which means that the area of its base must be. Working backwards, you can figure out that the radius of a circle of areais. The circumference of a circle with a radius ofis, which is greater than.

Example Question #1 :Cylinders

What is the surface area of a cylinder that has a diameter of 6 inches and is 4 inches tall?

Possible Answers:

Correct answer:

Explanation:

The formula for the surface area of a cylinder is,

whereis the radius andis the height.

Example Question #1501 :Gre Quantitative Reasoning

A cylinder has a radius of 4 and a height of 8. What is its surface area?

Possible Answers:

Correct answer:

Explanation:

This problem is simple if we remember the surface area formula!

Example Question #1 :Cylinders

Quantitative Comparison

Quantity A: Surface area of a cylinder that is 2 feet high and has a radius of 4 feet

Quantity B: Surface area of a box that is 3 feet wide, 2 feet high, and 4 feet long

Possible Answers:

The two quantities are equal.

Quantity A is greater.

The relationship cannot be determined from the information given.

Quantity B is greater.

Correct answer:

Quantity A is greater.

Explanation:

Quantity A: SA of a cylinder = 2πr2+ 2πrh= 2π *16 + 2π* 4 * 2 = 48π

Quantity B: SA of a rectangular solid = 2ab+ 2bc+ 2ac= 2 * 3 * 2 + 2 * 2 * 4 + 2 * 3 * 4 = 52

48πis much larger than 52, becauseπis approximately 3.14.

Example Question #1 :Solid Geometry

A cylinder has a height of 4 and a circumference of 16π. What is its volume

Possible Answers:

16π

128π

64π

none of these

256π

Correct answer:

256π

Explanation:

circumference = πd

d = 2r

volume of cylinder = πr2h

r = 8, h = 4

volume = 256π

Example Question #1 :How To Find The Volume Of A Cylinder

Rusty is considering making a cylindrical grain silo to store his crops. He has an area that is 6 feet long, 6 feet wide and 12 feet tall to build a cylinder in. What is the maximum volume of grain that he can store in this cylinder?

Possible Answers:

Correct answer:

Explanation:

The maximum cylindrical base can have a diameter of 6 and therefore a radius of 3. The formula for the volume of a cylinder is\ dpi{100} \ \小πr ^ {2} h, which in this case is\dpi{100} \small 3\times 3\times 12\times \pi.

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