SSAT Upper Level Math : How to find the volume of a tetrahedron

Study concepts, example questions & explanations for SSAT Upper Level Math

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Example Questions

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

In three-dimensional space, the four vertices of a tetrahedron - a solid with four faces - have Cartesian coordinates \(\displaystyle (0,0,0), (10,0,0), (5, 18, 0), (8,8,8)\).

Give its volume.

Possible Answers:

\(\displaystyle 360\)

\(\displaystyle 160\)

\(\displaystyle 240\)

\(\displaystyle 120\)

\(\displaystyle 720\)

Correct answer:

\(\displaystyle 240\)

Explanation:

A tetrahedron is a triangular pyramid and can be looked at as such.

Three of the vertices - \(\displaystyle (0,0,0), (10,0,0), (5, 18, 0)\) - are on the \(\displaystyle xy\)-plane, and can be seen as the vertices of the triangular base. This triangle, as seen below, is isosceles:

Tetrahedron

Its base is 10 and its height is 18, so its area is

\(\displaystyle B = \frac{1}{2} \cdot 10 \cdot 18 = 90\)

The fourth vertex is off the \(\displaystyle xy\)-plane; its perpendicular distance to the aforementioned face is its \(\displaystyle z\)-coordinate, 8, so this is the height of the pyramid. The volume of the pyramid is 

\(\displaystyle V = \frac{1}{3} \cdot 90 \cdot 8 = 240\)

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

In three-dimensional space, the four vertices of a tetrahedron - a solid with four faces - have Cartesian coordinates \(\displaystyle (0,0,0), (15,0,0), (0,15,0), (0,0, 15)\).

What is the volume of this tetrahedron?

Possible Answers:

\(\displaystyle 281\frac{1}{4}\)

\(\displaystyle 843 \frac{3}{4}\)

\(\displaystyle 375\)

The correct answer is not among the other responses.

\(\displaystyle 562 \frac{1}{2}\)

Correct answer:

\(\displaystyle 562 \frac{1}{2}\)

Explanation:

The tetrahedron looks like this:

Tetrahedron

\(\displaystyle O\) is the origin and \(\displaystyle A,B,C\) are the other three points, which are fifteen units away from the origin on each of the three (perpendicular) axes.

This is a triangular pyramid, and we can consider \(\displaystyle \Delta OCB\) the base; its area is half the product of its legs, or

\(\displaystyle B = \frac{1}{2} \cdot 15 \cdot 15 = 112\frac{1}{2}\).

The volume of the tetrahedron is one third the product of its base and its height, the latter of which is 15. Therefore,

\(\displaystyle V = \frac{1}{3} \cdot 15 \cdot 112\frac{1}{2} = 562 \frac{1}{2}\).

Example Question #3 : How To Find The Volume Of A Tetrahedron

Tetrahedron

Above is the base of a triangular pyramid, which is equilateral. The height of the pyramid is equal to the perimeter of its base. In terms of \(\displaystyle n\), give the volume of the pyramid.

Possible Answers:

\(\displaystyle \frac{2 n^{3} }{9}\)

\(\displaystyle \frac{2 n^{3} \sqrt{3}}{9}\)

\(\displaystyle \frac{2 n^{3} \sqrt{3}}{3}\)

\(\displaystyle \frac{2 n^{3} }{3}\)

\(\displaystyle 2n^{3}\)

Correct answer:

\(\displaystyle \frac{2 n^{3} }{3}\)

Explanation:

By the 30-60-90 Theorem, \(\displaystyle AM = CM \sqrt{3}\), or

\(\displaystyle CM = \frac{AM}{\sqrt{3}} = \frac{n}{\sqrt{3}} = \frac{n\sqrt{3}}{3}\)

\(\displaystyle M\) is the midpoint of \(\displaystyle \overline{BC}\), so

\(\displaystyle BC = 2 \cdot CM = 2 \cdot \frac{n\sqrt{3}}{3} = \frac{2n\sqrt{3}}{3}\)

The area of the triangular base is half the product of its base and its height:

\(\displaystyle B = \frac{1}{2} \cdot n \cdot \frac{2n\sqrt{3}}{3}= \frac{ n^{2}\sqrt{3}}{3}\)

The height of the pyramid is equal to the perimeter, so it will be three times \(\displaystyle BC\), or 

\(\displaystyle p = 3 \cdot BC = 3 \cdot \frac{2n\sqrt{3}}{3} = 2n\sqrt{3}\)

The volume of the pyramid is one third the product of this area and the height of the pyramid:

\(\displaystyle V = \frac{1}{3} \cdot 2n\sqrt{3} \cdot \frac{ n^{2}\sqrt{3}}{3}\)

\(\displaystyle = \frac{2 n^{3}\cdot \sqrt {3} \cdot \sqrt{3}}{9}\)

\(\displaystyle = \frac{6 n^{3} }{9}\)

\(\displaystyle = \frac{2 n^{3} }{3}\)

Example Question #4 : How To Find The Volume Of A Tetrahedron

In three-dimensional space, the four vertices of a tetrahedron - a solid with four faces - have Cartesian coordinates

\(\displaystyle (0,0,0), (n-1,0,0), (0,n,0), (0,0, n+1)\)

where \(\displaystyle n > 1\)

Give its volume in terms of \(\displaystyle n\).

Possible Answers:

\(\displaystyle \frac{1}{6} n^{3}-\frac{1}{6}\)

\(\displaystyle \frac{1}{6} n^{3}- \frac{1}{3}n^{2} -\frac{1}{6}n\)

\(\displaystyle \frac{1}{6} n^{3}\)

\(\displaystyle \frac{1}{6} n^{3}- \frac{1}{3}n^{2} +\frac{1}{6}n\)

\(\displaystyle \frac{1}{6} n^{3}-\frac{1}{6}n\)

Correct answer:

\(\displaystyle \frac{1}{6} n^{3}-\frac{1}{6}n\)

Explanation:

The tetrahedron looks like this:

Tetrahedron

\(\displaystyle O\) is the origin and \(\displaystyle A,B,C\) are the other three points.

This is a triangular pyramid, and we can consider \(\displaystyle \Delta OCB\) the base; its area is half the product of its legs, or

\(\displaystyle B = \frac{1}{2} \cdot (n-1)\cdot n\).

The volume of the tetrahedron is one third the product of its base and its height. Therefore, 

\(\displaystyle V = \frac{1}{3} \cdot \left ( n+1\right ) \cdot \frac{1}{2} \cdot (n-1)\cdot n\)

After some rearrangement:

\(\displaystyle V= \frac{1}{6} ( n+1 ) (n-1) n\)

\(\displaystyle = \frac{1}{6} (n^{2}-1) n\)

\(\displaystyle = \frac{1}{6} (n^{3}-n)\)

\(\displaystyle = \frac{1}{6} n^{3}-\frac{1}{6}n\)

Example Question #5 : How To Find The Volume Of A Tetrahedron

In three-dimensional space, the four vertices of a tetrahedron - a solid with four faces - have Cartesian coordinates

\(\displaystyle (0,0,0), (n ,0,0), (0,2n,0), (0,0, 3n)\)

where \(\displaystyle n > 1\)

Give its volume in terms of \(\displaystyle n\).

Possible Answers:

\(\displaystyle 3 n^{3}\)

\(\displaystyle \frac{ 3 n^{3}}{2}\)

\(\displaystyle \frac{2 n^{3}}{3}\)

\(\displaystyle 2 n^{3}\)

\(\displaystyle n^{3}\)

Correct answer:

\(\displaystyle n^{3}\)

Explanation:

The tetrahedron looks like this:

Tetrahedron

\(\displaystyle O\) is the origin and \(\displaystyle A,B,C\) are the other three points, each of which lies along one of the three (mutually perpendicular) axes.

This is a triangular pyramid, and we can consider \(\displaystyle \Delta OAB\) the base; its area is half the product of its legs, or

\(\displaystyle B = \frac{1}{2} \cdot n \cdot 2n = n^{2}\).

The volume of the tetrahedron is one third the product of its base area \(\displaystyle n^{2}\) and its height \(\displaystyle 3n\). Therefore, the volume is 

\(\displaystyle V = \frac{1}{3} \cdot3n \cdot n^{2} = n^{3}\)

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

Find the volume of a regular tetrahedron that has a side length of \(\displaystyle 5\).

Possible Answers:

\(\displaystyle \frac{5\sqrt2}{6}\)

\(\displaystyle \frac{25\sqrt2}{12}\)

\(\displaystyle \frac{125\sqrt2}{12}\)

\(\displaystyle 20\sqrt2\)

Correct answer:

\(\displaystyle \frac{125\sqrt2}{12}\)

Explanation:

Use the following formula to find the volume of a regular tetrahedron:

\(\displaystyle \text{Volume}=\frac{\sqrt2}{12}side^3\)

Now, plug in the given side length.

\(\displaystyle \text{Volume}=\frac{\sqrt2}{12}5^3\)

\(\displaystyle \text{Volume}=\frac{125\sqrt2}{12}\)

 

 

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

Find the volume of a regular tetrahedron that has a side length of \(\displaystyle 4\).

Possible Answers:

\(\displaystyle \frac{16\sqrt2}{3}\)

\(\displaystyle 32\sqrt2\)

\(\displaystyle \frac{8\sqrt2}{3}\)

\(\displaystyle \frac{64}{3\sqrt2}\)

Correct answer:

\(\displaystyle \frac{16\sqrt2}{3}\)

Explanation:

Use the following formula to find the volume of a regular tetrahedron:

\(\displaystyle \text{Volume}=\frac{\sqrt2}{12}side^3\)

Now, plug in the given side length.

\(\displaystyle \text{Volume}=\frac{\sqrt2}{12}4^3\)

\(\displaystyle \text{Volume}=\frac{64\sqrt2}{12}\)

\(\displaystyle \text{Volume}=\frac{16\sqrt2}{3}\)

 

 

Example Question #8 : How To Find The Volume Of A Tetrahedron

Find the volume of a regular tetrahedron with a side length of \(\displaystyle 6\).

Possible Answers:

\(\displaystyle 36\sqrt2\)

\(\displaystyle 18\sqrt2\)

\(\displaystyle 6\sqrt2\)

\(\displaystyle 24\sqrt2\)

Correct answer:

\(\displaystyle 18\sqrt2\)

Explanation:

Use the following formula to find the volume of a regular tetrahedron:

\(\displaystyle \text{Volume}=\frac{\sqrt2}{12}side^3\)

Now, plug in the given side length.

\(\displaystyle \text{Volume}=\frac{\sqrt2}{12}6^3\)

\(\displaystyle \text{Volume}=\frac{216\sqrt2}{12}\)

\(\displaystyle \text{Volume}=18\sqrt2\)

 

 

Example Question #9 : How To Find The Volume Of A Tetrahedron

Find the volume of a regular tetrahedron with side lengths of \(\displaystyle 7\).

Possible Answers:

\(\displaystyle \frac{7\sqrt2}{6}\)

\(\displaystyle \frac{343\sqrt2}{12}\)

\(\displaystyle 18\sqrt2\)

\(\displaystyle \frac{49\sqrt2}{12}\)

Correct answer:

\(\displaystyle \frac{343\sqrt2}{12}\)

Explanation:

Use the following formula to find the volume of a regular tetrahedron:

\(\displaystyle \text{Volume}=\frac{\sqrt2}{12}side^3\)

Now, plug in the given side length.

\(\displaystyle \text{Volume}=\frac{\sqrt2}{12}7^3\)

\(\displaystyle \text{Volume}=\frac{343\sqrt2}{12}\)

 

Example Question #10 : How To Find The Volume Of A Tetrahedron

Find the volume of a regular tetrahedron with side lengths of \(\displaystyle 8\).

Possible Answers:

\(\displaystyle 10\sqrt2\)

\(\displaystyle 2\sqrt2\)

\(\displaystyle \frac{16\sqrt2}{3}\)

\(\displaystyle \frac{128\sqrt2}{3}\)

Correct answer:

\(\displaystyle \frac{128\sqrt2}{3}\)

Explanation:

Use the following formula to find the volume of a regular tetrahedron:

\(\displaystyle \text{Volume}=\frac{\sqrt2}{12}side^3\)

Now, plug in the given side length.

\(\displaystyle \text{Volume}=\frac{\sqrt2}{12}8^3\)

\(\displaystyle \text{Volume}=\frac{512\sqrt2}{12}\)

\(\displaystyle \text{Volume}=\frac{128\sqrt2}{3}\)

 

 

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