GMAT Math : Tetrahedrons

年代tudy concepts, example questions & explanations for GMAT Math

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Example Questions

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Example Question #1 :Dsq: Calculating The Length Of An Edge Of A Tetrahedron

Find the length of the edge of a tetrahedron.

年代tatement 1: The volume is 6.

年代tatement 2: The surface area is 6.

Possible Answers:

Correct answer:

Explanation:

年代tatement 1:) The volume is 6.

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

考虑到体积,可以找到边缘of the tetrahedron.

年代tatement 2:) The surface area is 6.

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

年代ubstitute the surface area to find the edge.

Therefore:

Example Question #1 :Dsq: Calculating The Volume Of A Tetrahedron

Pyramid 1 in three-dimensional coordinate space has as its base the square with vertices at the origin,,, and, and its apex at the point;Pyramid 2 has as its base the square with vertices at the origin,,, and, and its apex at the point.All six variables represent positive quantities. Which pyramid has the greater volume?

年代tatement 1:and

年代tatement 2:

Possible Answers:

BOTH statements TOGETHER are insufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

声明1单独是充分的回答这个问题tion, but Statement 2 ALONE is NOT sufficient to answer the question.

年代tatement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Correct answer:

年代tatement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Explanation:

The volume of a pyramid is one third the product of its height and the area its base. The two pyramids have the same base, so the pyramid with the greater height will have the greater volume (and if their heights are equal, their volumes are equal).

Pyramid 1 is shown below:

Pyramid

The base of the pyramid is on the-plane, so the height of the pyramid is the perpendicular distance from apexto this plane; this is the协调,.The base of the pyramid is a square of sidelength 10, so its area is the square of 10, or 100. This makes the volume of Pyramid 1

年代imilarly, the volume of Pyramid 2 is

Therefore, the problem asks us to determine which ofandis the greater.

Assume Statement 1 alone. Since, we can multiply all expressions byto get a range for the volume of Pyramid 1:

年代imilarly, since, we can multiply all expressions by 36 to get a range of values for the volume of Pyramid 2:

年代ince the two ranges share values, it cannot be determined for certain which pyramid has the greater volume.

Assume Statement 2 alone. Then, sinceand, it easily follows that

,

and, subsequently, Pyramid 2 has the greater volume.

Example Question #2 :Dsq: Calculating The Volume Of A Tetrahedron

Pyramid_2

Note: Figure NOT drawn to scale, but you may assumeand

In the above figure, a pyramid with a rectangular base is inscribed inside a rectangular prism; its vertices are.What is the volume of the pyramid?

年代tatement 1: 30-60-90 trianglehas area

年代tatement 2: Isosceles right trianglehas area 50.

Possible Answers:

声明1单独是充分的回答这个问题tion, but Statement 2 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

年代tatement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

Correct answer:

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Explanation:

The volume of the pyramid is one third the product of heightand the area of its rectangular base, which is;that is,

Assume Statement 1 alone.has area, which is half the product of the length of shorter legand longer leg.Also, by the 30-60-90 Theorem,, so, combining these statements,

, and

However, we do not have any way of finding out, so the volume cannot be calculated.

Assume Statement 2 alone.is isosceles, so;again, since the area of a right triangle is half the product of the lengths of its legs,

However, we have no way of finding out

The two statements together give all three of,, and, so the volume can be calculated as

Example Question #3 :Dsq: Calculating The Volume Of A Tetrahedron

A solid in three-dimensional coordinate space has four vertices, at points,,, andfor some positive values of.What is the volume of the solid?

年代tatement 1:

年代tatement 2:

Possible Answers:

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

声明1单独是充分的回答这个问题tion, but Statement 2 ALONE is NOT sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

年代tatement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Correct answer:

年代tatement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Explanation:

The figure described is the triangular pyramid, or tetrahedron, in the coordinate three-space below.

Tetrahedron

The base of the pyramid can be seen as a triangle with the three known coordinates,, and, and the area of its base is half the product of the lengths of its legs, which is

The volume of the pyramid is one third the product of the area of its base, which is 48, and its height, which is the perpendicular distance from the unknown point to the base. Since the base is entirely within the-plane, this distance is the-coordinate of the apex, which is.因此,唯一需要潜艇雷达rmine the volume of the pyramid is;this information is provided in Statement 2, but not Statement 1.

Example Question #4 :Dsq: Calculating The Volume Of A Tetrahedron

Tetra_1

In the above diagram, a tetrahedron - a triangular pyramid - with verticesis shown inside a cube. Give the volume of the tetrahedron.

年代tatement 1: The perimeter of Squareis 16.

年代tatement 2: The area ofis 8.

Possible Answers:

BOTH statements TOGETHER are insufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

声明1单独是充分的回答这个问题tion, but Statement 2 ALONE is NOT sufficient to answer the question.

年代tatement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Correct answer:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

The volume of the pyramid is one third the product of heightand the area of its base, which in turn, since here it is a right triangle, is half the product of the lengthsandof its legs. Since the prism in the figure is a cube, the three lengths are equal, so we can set each to.The volume of the pyramid is

Therefore, knowing the length of one edge of the cube is sufficient to determine the volume of the pyramid.

Assume Statement 1 alone. Since the perimeter of Squareis 16, each side of the square, and each edge of the cube has one fourth this measure, or 4.

Assume Statement 2 alone.has congruent legs, each of measure;面积8日以来can be found as follows:

From either statement alone, the length of each side of the cube, and, subsequently, the volume of the pyramid, can be calculated.

Example Question #5 :Dsq: Calculating The Volume Of A Tetrahedron

Tetra_1

Note: Figure NOT drawn to scale.

Refer to the above figure, which shows a tetrahedron, or triangular pyramid. What is the volume of the tetrahedron?

年代tatement 1:is an isosceles triangle with area 64.

年代tatement 2:is an equilateral triangle with perimeter 48.

Possible Answers:

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

年代tatement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

声明1单独是充分的回答这个问题tion, but Statement 2 ALONE is NOT sufficient to answer the question.

Correct answer:

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Explanation:

Each statement gives enough information about one triangle to determine its area, its angles, and its sidelengths, but no information about the other three triangles is given except for one side.

Assume both statements are known.is an isosceles triangle with area 64. Since, we can find this common sidelength using the area formula for a triangle, with these lengths as height and base:

This is the length of bothand

By the 45-45-90 Theorem,has lengthtimes this, or

年代inceis an equilateral triangle,.年代inceis a right triangle,, and, the triangle is also isosceles, and;by a similar argument,

The volume of the pyramid can be calculated. Its base, which is congruent to, has area 64, and its height is;multiply one third by their product to get the volume.

Example Question #6 :Dsq: Calculating The Volume Of A Tetrahedron

Pyramid 1 in three-dimensional coordinate space has as its base the square with vertices at the origin,,, and, and its apex at the point;Pyramid 2 has as its base the square with vertices at the origin,,, and, and its apex at the point.All six variables represent positive quantities. Which pyramid has the greater volume?

年代tatement 1:

年代tatement 2:

Possible Answers:

声明1单独是充分的回答这个问题tion, but Statement 2 ALONE is NOT sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

年代tatement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Correct answer:

声明1单独是充分的回答这个问题tion, but Statement 2 ALONE is NOT sufficient to answer the question.

Explanation:

The volume of a pyramid is one third the product of its height and the area its base.

Pyramid 1 is shown below:

Pyramid

The base of the pyramid is on the-plane, so the height of the pyramid is the perpendicular distance from apexto this plane; this is the协调,.The base of the pyramid is a square of sidelength 10, so its area is the square of 10, or 100. This makes the volume of Pyramid 1

年代imilarly, the volume of Pyramid 2 is

The problem therefore asks us which, if either, oftois the greater quantity.

Assume Statement 1 alone. If, then, and

年代ince, it follows that, and- that is, Pyramid 2 has the greater volume.

表述二单独予以足够的信息。We take two sets of values ofandthat add up to 25:

Case 1:

In this case, Pyramid 2 has the greater heightandthe greater base area, so it easily follows that Pyramid 2 has the greater volume.

Case 2:

Then the volume of Pyramid 1 is

and that of Pyramid 2 is

This makes Pyramid 1 the greater in volume.

Example Question #7 :Dsq: Calculating The Volume Of A Tetrahedron

Pyramid_2

Note: Figure NOT drawn to scale, but you may assume

In the above figure, a pyramid with a rectangular base is inscribed inside a rectangular prism; its vertices are.What is the volume of the pyramid?

年代tatement 1: The hypotenuseof 30-60-90 trianglehas length 16.

年代tatement 2: The hypotenuseof 45-45-90 right trianglehas length

Possible Answers:

声明1单独是充分的回答这个问题tion, but Statement 2 ALONE is NOT sufficient to answer the question.

年代tatement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Correct answer:

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Explanation:

The volume of the pyramid is one third the product of heightand the area of its rectangular base, which is;that is,

Assume Statement 1 alone.is a 30-60-90 triangle with a hypotenuse of length 16. By the 30-60-90 Triangle Theorem, short leghas length half this, or 8, and long leghas lengthtimes that of, or.However, the length ofcannot be determined.

Assume Statement 2 alone.is a 45-45-90 right triangle with a hypotenuse of length.By the 45-45-90 Theorem, its legsandeach have lengthdivided by, which is;however, the length ofcannot be determined.

From the two statements together, we can determine thatand, and calculate the volume:

Example Question #8 :Dsq: Calculating The Volume Of A Tetrahedron

Tetra_3

Note: Figure NOT drawn to scale.

The above figure shows a rectangular prism with an inscribedtetrahedron,or triangular pyramid, with vertices.What is the volume of the tetrahedron?

年代tatement 1: Isosceles right trianglehas area 32.

年代tatement 2:

Possible Answers:

声明1单独是充分的回答这个问题tion, but Statement 2 ALONE is NOT sufficient to answer the question.

年代tatement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Correct answer:

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Explanation:

The volume of the pyramid is one third the product of the height, which is, and the area of the base; this base, being a right triangle, is equal to one half the product of the lengths of its legs, orand.Therefore,

or

From Statement 1 alone, we knowis isosceles and has area 32; therefore, its common leg length can be determined using the area formula:

Therefore,.However, nothing can be determined about

年代tatement 2 alone does not give any of the three desired lengths or any information necessary to find them.

However, Statement 2, along with the information from Statement 1, can be used to find.From Statement 2,, and from Statement 1,;the Pythagorean Theorem can be used to find.Therefore, all three of,, andcan be found, and the volume of the pyramid can be calculated.

Example Question #9 :Dsq: Calculating The Volume Of A Tetrahedron

A regular tetrahedron is a solid with four faces, each of which is an equilateral triangle.

Give the volume of a regular tetrahedron.

年代tatement 1: Each edge has length 8.

年代tatement 2: Each face has area

Possible Answers:

声明1单独是充分的回答这个问题tion, but Statement 2 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

年代tatement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

Correct answer:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

The formula for the volume of a regular tetrahedron given the length of each edgeis

年代tatement 1 givesinformation explicitly. Statement 2 gives the means to find, since, ifis substituted forin the formula for an equilateral triangle:

,

the value ofcan be determined.

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