GMAT Math : Calculating the volume of a cube

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Example Questions

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Example Question #835 : Gmat Quantitative Reasoning

The distance from one vertex of a cube to its opposite vertex is one foot. Give the volume of the cube.

Possible Answers:

Correct answer:

Explanation:

Since we are looking at inches, we will look at one foot as twelve inches.

Let  be the length of one edge of the cube. By the three-dimensional extension of the Pythagorean Theorem, 

 inches.

Cube this sidelength to get the volume:

 cubic inches.

Example Question #831 : Gmat Quantitative Reasoning

A cubic pool is usually filled at about  of its total volume. If one side of the pool is m, how many liters of water will fill the pool to the desired capacity?

Possible Answers:

Correct answer:

Explanation:

To find the volume of a cube we use the formula:

In our case the total volume of the pool is 10cubic meters.

Filling the pool to 95% of its total volume will require:  cubic meters.

Now we need to convert from cubic meters to liters in order to answer the question.

Remember  cubic meter =  liters.

Thus,

.

Therefore, the number of liters of water needed is 950000 liters.

 

Example Question #837 : Gmat Quantitative Reasoning

A sphere of surface area  is inscribed inside a cube. Give the volume of the cube.

Possible Answers:

The correct answer is not given among the other responses.

Correct answer:

Explanation:

The diameter of a sphere is equal to the length of an edge of the cube in which it is inscribed. We can derive the radius using the formula for the surface area of a sphere:

Substituting in the given value:

Dividing each side by :

Taking the square root of each side:

The diameter is twice this, or . This is the length of the edge of the cube, so we can cube it to get the volume:

Example Question #838 : Gmat Quantitative Reasoning

A sphere with surface area  circumscribes a cube. Give the volume of the cube.

Possible Answers:

The correct answer is not given among the other responses.

Correct answer:

The correct answer is not given among the other responses.

Explanation:

The diameter of a sphere is equal to the length of a diagonal of the cube it circumscribes. We can derive the radius using the formula for the volume of a sphere, but first, we have to solve for the radius using the formula for the surface area of a sphere:

The diameter is twice this, or . This is the length of the diagonal of the cube. By the three-dimensional extension of the Pythagorean Theorem,

 

The volume is the cube of this:

, which is not given as one of the choices.

Example Question #839 : Gmat Quantitative Reasoning

A cube has a volume of  cubic feet. If the length of each side of the cube is doubled, what is its new volume, in cubic feet?

Possible Answers:

Correct answer:

Explanation:

One way we can solve this problem is by first determining the dimensions of the original cube. By definition, the length, width, and depth of a cube are equal, so if the original volume is 8 cubic feet, then:

We then double the length of each side of the original cube, so the length of each side of the new cube is:

Now we can use the dimensions of our new cube to find its volume:

So if we double the dimensions of the original cube, the resulting cube has a volume that is eight times greater, 64 cubic feet.

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