GRE Math : Solid Geometry

Study concepts, example questions & explanations for GRE Math

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Example Questions

Example Question #2 : How To Find The Volume Of A Cylinder

A cylinder with volume of  and a radius of  has its radius doubled. What is the volume of the new cylinder?

Possible Answers:

Correct answer:

Explanation:

To begin, you must solve for the height of the original cylinder. We know:

For our values, we know:

Now, divide both sides by :

So, if we have a new radius of , our volume will be:

Example Question #11 : Solid Geometry

If the dimensions of a rectangular crate are , which of the following CANNOT be the total surface area of two sides of the crate?

Possible Answers:

Correct answer:

Explanation:

Side 1: surface area of the 6 x 7 side is 42

Side 2: surface area of the 7 x 8 side is 56

Side 3: surface area of the 6 x 8 side is 48.

We can add sides 1 and 3 to get 90, so that's not the answer.

We can add sides 1 and 1 to get 84, so that's not the answer.

We can add sides 2 and 3 to get 104, so that's not the answer.

We can add sides 2 and 2 to get 112, so that's not the answer.

This leaves the answer of 92. Any combination of the three sides of the rectangular prism will not give us 92 as the total surface area.

Example Question #314 : Geometry

Kate wants to paint a cylinder prism.

What is the surface area of her prism if it is  inches tall and has a diameter of  inches? Round to the nearest whole number.

Possible Answers:

Correct answer:

Explanation:

First, find the area of the base of the cyclinder:

 and multiply that by two, since there are two sides with this measurement: 

Then, you find the width of the rectangular portion (label portion) of the prism by finding the circumference of the cylinder: 

. This is then multiplied by the height of the cylinder to find the area of the rectanuglar portion of the cylinder: .

Finally, add all sides together and round: .

Example Question #2 : How To Find The Surface Area Of A Prism

Prism_1_454590This triangular prism has a height of  feet and a length of  feet.

What is the surface area of the prism? Round to the nearest tenth.

Possible Answers:

Correct answer:

Explanation:

Find the area of the triangular sides first: 

 

Since there are two sides of this area, we multiply the area by 2: 

 

Next find the area of the rectangular regions. Two of them have the width of 3 feet and a length of 7 feet, while the last one has a width measurement of  feet and a length of 7 feet. Multiply and add all other sides: 

.

Lastly, add the triangular sides to the rectangular sides and round: 

.

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

A rectangular prism has a width of 3 units, a length that is twice the width, and a height that is two-thirds the length. What is the volume of the prism?

Possible Answers:

 

 

 

 

Correct answer:

 

Explanation:

Remember, the formula for the volume of a rectangular prism is width times height times length:

Now, let's solve the word problem for each of these values. We know that . If length is double the width, then the length must be 6 units. If the height is two-thirds the length, then the height must be 4:

Multiply all three values together to solve for the volume:

 

The volume of the rectangular prism is  units cubed.

Example Question #321 : Geometry

The surface area of a rectangular prism is , and the lengths of two sides are  and . What is the volume of the prism?

Possible Answers:

Correct answer:

Explanation:

The surface area of a rectangular prism with sides , and  is given as:

Two sides are known; it does not matter how they are designated, but for this problem let  and , with  as the unknown side. This yields equality:

Now that the three dimensions are known, it's possible to calculate the volume:

Example Question #1 : Cubes

Quantity A: The length of a side of a cube with a volume of  .

Quantity B: The length of a side of a cube with surface area of  .

Which of the following is true?

Possible Answers:

The two quantities are equal

Quantity A is larger.

The relationship between the two quantities cannot be determined.

Quantity B is larger.

Correct answer:

The two quantities are equal

Explanation:

Recall that the equation for the volume of a cube is:

Since the sides of a cube are merely squares, the surface area equation is just  times the area of one of those squares:

So, for our two quantities:

 

Quantity A

Use your calculator to estimate this value (since you will not have a square root key). This is .

 

Quantity B

First divide by :

Therefore, 

Therefore, the two quantities are equal.

Example Question #1 : How To Find The Length Of An Edge Of A Cube

What is the length of an edge of a cube with a surface area of ?

Possible Answers:

Correct answer:

Explanation:

The surface area of a cube is made up of  squares. Therefore, the equation is merely  times the area of one of those squares.  Since the sides of a square are equal, this is:

, where  is the length of one side of the square.

For our data, we know:

This means that:

Now, while you will not have a calculator with a square root key, you do know that . (You can always use your calculator to test values like this.) Therefore, we know that . This is the length of one side

Example Question #17 : Solid Geometry

If a cube has a total surface area of  square inches, what is the length of one edge?

Possible Answers:

There is not enough information given.

 

Correct answer:

 

Explanation:

There are 6 sides to a cube. If the total surface area is 54 square inches, then each face must have an area of 9 square inches.

Every face of a cube is a square, so if the area is 9 square inches, each edge must be 3 inches.

Example Question #1 : How To Find The Diagonal Of A Cube

The surface area of a cube is 486 units.  What is the distance of its diagonal (e.g. from its front-left-bottom corner to its rear-right-top corner)?

Possible Answers:

81

None of the others

9√(3)

9√(2)

9

Correct answer:

9√(3)

Explanation:

First, we must ascertain the length of each side.  Based on our initial data, we know that the 6 faces of the cube will have a surface area of 6x2. This yields the equation:

6x2 = 486, which simplifies to: x2 = 81; x = 9.

Therefore, each side has a length of 9.  Imagine the cube is centered on the origin.  This means its "front-left-bottom corner" will be at (–4.5, –4.5, 4.5) and its "rear-right-top corner" will be at (4.5, 4.5, –4.5).  To find the distance between these, we use the three-dimensional distance formula:

d = √((x1 – x2)2 + (y1 – y2)2 + (z1 – z2)2)

For our data, this will be:

√( (–4.5 – 4.5)2 + (–4.5 – 4.5)2 + (4.5 + 4.5)2) =

√( (–9)2 + (–9)2 + (9)2) = √(81 + 81 + 81) = √(243) =

√(3 * 81) = √(3) * √(81) = 9√(3)

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