Rectangular Solids & Cylinders - GMAT Quantitative Reasoning

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Question

is a cube. What is the length of diagonal ?

(1) The area of a face of the cube is .

(2) The length of is .

Answer

To know the diagonal HB of the cube, we need to have information about the length of the edges of the cube. Knowing the area of a face would allow us to find the length of an edge; therefore statement 1 alone is sufficient.

Statment 2 alone is sufficient as well since the length of a diagonal of a square is given by , where is the length of a side of the square and ultimately we can find the length of an edge of the square.

Therefore each statement alone is sufficient.

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Question

Calculate the diagonal of a cube.

  1. The surface area of the cube is .
  2. The volume of the cube is .

Answer

Statement 1: We can use the surface area to find the length of the cube's edge and then determine the length of the diagonal.

where represents the length of the cube's edge

Now that we know the length of the edge, we can find the length of the diagonal: .

Statement 2: Once again, we can use the provided information to find the length of the cube's edge.

Which means the length of the diagonal is .

Thus, each statement alone is sufficient to answer the question.

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Question

Give the length of the diagonal of the cube.

  1. The surface area of the cube is .
  2. The volume of the cube is .

Answer

Statement 1: To find the length of the diagonal of the cube we need to find the length of the cube's edge. We can use the given surface area value to do so:

Now that we know the length of the cube's edge, we can calculate the diagonal:

Statement 2: We're given the volume of the cube which we can also use to solve for the length of the cube's edge.

Knowing the length of the cube's edge allows us to calculate the diagonal:

Each statement alone is sufficient to answer the question.

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Question

Find the diagonal of the cube.

  1. The surface area of the cube is .
  2. The length of an edge of the cube measures .

Answer

Statement 1: We need the length of an edge in order to find the diagonal of the cube. Luckily, we can find the length using the information provided:

Now that we know the length of an edge is 11 cm we can find the length of the diagonal.

Statement 2: We're given the information we need to find the diagonal, all we need to do is plug it into the equation

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Question

What is the length of the diagonal of the cube A if the diagonal of cube B is ?

  1. The lengths of the edges of cube A to cube B is a ratio of 1:2.
  2. The surface area of cube A is .

Answer

Statement 1: The information provided in the question is only useful if we're given a relationship between cube A and cube B. Since this statement does provide us with the ratio of 1:2,we can answer the question.

where represents the length of the cube's edge

we can easily see the length measures

Remember the ratio of cube A to cube B is 1:2.

Now that we know the length, we can find the diagonal of the cube:

Statement 2: We're given information about cube A so we don't need to worry about cube B. Using this information we can solve for the edge length of cube A and then calculate the diagonal.

Knowing the length of the edge allows us to find the diagonal of the cube

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Question

Find the length of the diagonal of cube .

I) has a volume of .

II) has a surface area of .

Answer

To find the length of the diagonal, we need the side length.

I) Gives us the volume of the cube. Take the cubed root to find the side length.

II) Gives us the surface area, divide by 6 (the number of faces in a cube) and take the square root to find the side length.

Diagonal of a cube is the side length times the square root of three. Alternatively, this can be found using the Pythagorean Theorem twice.

Either way, we can use I) or II) to find our side lenght and then our diagonal.

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Question

What is the diagonal of a rectangular prism?

  1. Its surface area is

  2. Its height = twice its width = thrice its length.

Answer

The diagonal of a rectangular prism is found via the formula

The second statement reduces this to

However, the actual length is unknown. Statement 1 allows the calculation of a numerical value:

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Question

What is the length of the edge of a cube?

  1. Its volume is 1,728 cubic meters.

  2. Its surface area is 864 square meters

Answer

Call the sidelength, surface area, and volume of the cube , , and , respectively.

Then

or, equivalently,

So, given statement 1 alone - that is, given only the volume, you can demonstrate the sidelength to be

Also,

or, equivalently,

Given statement 2 alone - that is, given only the surface area, you can demonstrate the sidelength to be

Therefore, the answer is that either statement alone is sufficient.

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Question

A sphere is inscribed inside a cube. What is the volume of the sphere?

Statement 1: The surface area of the cube is 216.

Statement 2: The volume of the cube is 216.

Answer

The diameter of a sphere inscribed inside a cube is equal to the length of one of the edges of a cube. From either the surface area or the volume of a cube, the appropriate formula can be used to calculate this length. Half this is the radius, from which the formula can be used to find the volume of the sphere.

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Question

What is the length of edge of cube ?

(1) .

(2) .

Answer

In order to find the length of an edge, we would need any information about one of the faces of the cube or about the diagonal of the cube.

Statement 1 gives us the length of the diagonal of the cube, since the formula for the diagonal is where is the length of an edge of the cube and is the length of the diagonal we are able to find the length of the edge. Therefore statement 1 alone is sufficient.

Statement 2 alones is insufficient, it gives us something we can already tell knowing that ABCDEFGH is a cube.

Statement 1 alone is sufficient.

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Question

is a cube. What is the length of edge ?

(1) The volume of the cube is .

(2) The area of face is .

Answer

Like we have previously seen, to find the length of an edge, we need to have information about the other faces or anything else within the cube.

Statement 1 tells us that the volume of the cube is , from this we can find the length of the side of the cube. Statement 1 alone is sufficient.

Statement 2, tells us that the area of ABCD is , similarily, by taking the square root of this number, we can find the length of the edge of the cube.

Therefore each statement alone is sufficient.

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Question

Find the length of an edge of the cube.

  1. The volume of the cube is .
  2. The surface area of the cube is .

Answer

Statement 1: Use the volume formula for a cube to solve for the side length.

where represents the length of the edge

Statement 2: Use the surface area formula for a cube to solve for the side length.

Each statement alone is sufficient to answer the question.

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Question

A carpenter is building a box to hold his tools. Find the legth of the second smallest side of the box.

I) The box will have a volume of .

II) The smallest side is half the length of the longest side and the middle side is three-quarters of the length of the longest side.

Answer

Volume of a prism is found by:

We are given the volume in statement I.

We are told how the sides relate in statement II.

Put together these two statements will allow us to set up an equation to find the middle side.

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Question

A pirate wants to hide all of his treasure. He commisions a local woodworker to build him a series of wooden chests of volume of . Find the length of the longest side given the following:

I) The shortest side will be the length of the medium side.

II) The middle side will be 2 feet long.

Answer

A pirate wants to hide all of his treasure. He commisions a local woodworker to build him a series of wooden chests of volume of . Find the length of the longest side given the following:

I) The shortest side will be the length of the medium side

II) The middle side will be 2 feet long

Use I) and II) to find the length of the smallest side

Next, use the short and medium sides, along with info in the prompt, to find the last side:

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Question

Find the height of a box used to ship a computer, given the following:

I) The computer, along with all the cushioning, will take up a space of .

II) The width of the box will be the length of the box.

Answer

Find the height of a box used to ship a computer, given the following:

I) The computer, along with all the cushioning, will take up a space of

II) The width of the box will be the length of the box

Begin by recalling the volume of a rectangular prism formula:

Where l,w and h are length, width and height.

Next, use II) to set up a relationship between w and l

Then, use the voume formula:

As you can see, we still have two unknowns, and no way of finding either.

Therefore, we do not have information.

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Question

Find the length of the edge of a tetrahedron.

Statement 1: The volume is 6.

Statement 2: The surface area is 6.

Answer

Statement 1:) The volume is 6.

Write the formula to find the edge of the tetrahedron given the volume.

Given the volume, it is possible to find the edge of the tetrahedron.

Statement 2:) The surface area is 6.

Write the formula to find the edge of the tetrahedron given the surface.

Substitute the surface area to find the edge.

Therefore:

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Question

Ron is making a box in the shape of a cube. He needs to know how much wood he needs. Find the surface area of the box.

I) The diagonal distance across the box will be equivalent to .

II) Half the length of one side is .

Answer

To find the surface area of a cube, we need the length of one side.

Statement I gives the diagonal, we can use this to find the length of one side.

Statement II gives us a clue about the length of one side; we can use that to find the full length of one side.

The following formula gives us the surface area of a cube:

Use Statement I to find the length of the side with the following formula, where is the diagonal and is the side length:

So, using Statement I, we find the surface area to be

Using Statement, we get that the length of one side is two times two:

Again, use the surface area formula to get the following:

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Question

Of a given cylinder and a given cube, which, if either, has the greater surface area?

Statement 1: Both the height of the cylinder and the diameter of its bases are equal to the length of one edge of the cube.

Statement 2: Each face of the cube has as its area four times the square of the radius of the bases of the cylinder.

Answer

The surface area of a cylinder, given height and radius of the bases , is given by the formula

The surface area of a cube, given the length of each edge, is given by the formula

.

Assume Statement 1 alone. Then and, since the diameter of a base is , the radius is half this, or . The surface area of the cylinder is, in terms of , equal to

.

Since , the cylinder has the greater area regardless of the actual measurements.

Assume Statement 2 alone. The cube has six faces with area , so its surface area is six times this, or . The surface area of the cylinder is ; however, without knowing anything aobout the height of the cylinder, we cannot compare the two surface areas.

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Question

Jiminy wants to paint one of his silos. One gallon of this paint covers about square feet. How many gallons will he need?

I) The radius of the silo is feet.

II) The height is times longer the radius.

Answer

Review our statements:

I) The radius of the silo is feet.

II) The height is times longer the radius

We need to find our surface area in order to find how many gallons we need. Surface area is given by:

So to find the surface area, we need the radius and the height, so both statments are needed here.

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Question

A tin can has a volume of .

I) The height of the can is inches.

II) The radius of the base of the can is inches.

What is the surface area of the can? (Assume it is a perfect cylinder)

Answer

To find surface area of a cylinder we need the radius and the height.

If we are given the volume, and either the radius or the height, we can work backwards to find the other dimension.

Since I and II give us the height and the radius, either statement can be used to find the surface area.

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