High School Math : Geometry

Study concepts, example questions & explanations for High School Math

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Example Questions

Example Question #2 : Pyramids

What is the sum of the number of vertices, edges, and faces of a square pyramid?

Possible Answers:

\displaystyle 26

\displaystyle 24

\displaystyle 18

\displaystyle 20

\displaystyle 14

Correct answer:

\displaystyle 18

Explanation:

A square pyramid has one square base and four triangular sides.

Vertices (where two or more edges come together):  5. There are four vertices on the base (one at each corner of the square) and a fifth at the top of the pyramid.

Edges (where two faces come together):  8. There are four edges on the base (one along each side) and four more along the sides of the triangular faces extending from the corners of the base to the top vertex.

Faces (planar surfaces):  5. The base is one face, and there are four triangular faces that form the top of the pyramid.

Total \displaystyle = 5 + 8 + 5 = 18

Example Question #2 : Pyramids

An architect wants to make a square pyramid and fill it with 12,000 cubic feet of sand. If the base of the pyramid is 30 feet on each side, how tall does he need to make it?

Possible Answers:

\displaystyle 13.3\ ft

\displaystyle 40\ ft

\displaystyle 26.7\ ft

\displaystyle 50\ ft

\displaystyle 30\ ft

Correct answer:

\displaystyle 40\ ft

Explanation:

Volume of Pyramid = 1/3 * Area of Base * Height

12,000 ft3 = 1/3 * 30ft * 30ft * H

12,000  = 300 * H

H = 12,000  / 300 = 40

H = 40 ft

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

The volume of a 6-foot-tall square pyramid is 8 cubic feet. How long are the sides of the base?

Possible Answers:

\displaystyle 4\ ft^{2}

\displaystyle 1.5\ ft

\displaystyle 2\ ft

\displaystyle 4\ ft

\displaystyle 2\ ft^{2}

Correct answer:

\displaystyle 2\ ft

Explanation:

Volume of a pyramid is

\displaystyle \frac{1}{3}\cdot (Area\ of\ the\ base)\cdot (height)

Thus:

\displaystyle 8=\frac{1}{3}\cdot (Area\ of\ the\ base)\cdot (6)

\displaystyle 8=2\cdot (Area\ of\ the\ base)

Area of the base is \displaystyle 4\ ft^{2}.

Therefore, each side is \displaystyle 2\ ft.

Example Question #6 : Pyramids

What is the surface are of a pyramid with a square base length of 15 and a slant height (the height from the midpoint of one of the side lengths to the top of the pyramid) of 12?

Possible Answers:

\displaystyle 585

\displaystyle 575

\displaystyle 555

\displaystyle 565

Correct answer:

\displaystyle 585

Explanation:

To find the surface area of a pyramid we must add the areas of all five of the shapes creating the pyramid together.

We have four triangles that all have the same area and a square that supports the pyramid.

To find the area of the square we take the side length of 15 and square it \displaystyle 15^{2}=225

The area of the square is  \displaystyle 225.

To find the area of the triangle we must use the equation for the area of a triangle which is \displaystyle \frac{base\times height}{2}

Plug in the slant height 12 as the height of the triangle and use the side length of the square 15 as the base in our equation to get

 \displaystyle \frac{1}{2}*15*12=90

The area of each triangle is \displaystyle 90.

We then multiply the area of each triangle by 4 to find the area of all four triangles \displaystyle 4*90=360.

The four triangles have a surface area of \displaystyle 360.

We add the surface area of the four triangles with the area of the square to get the answer for the surface area of the pyramid which is \displaystyle 360+225=585.

The answer is  \displaystyle 585.

Example Question #611 : Geometry

Find the surface area of the following pyramid.

Pyramid

Possible Answers:

\displaystyle 350m^2

\displaystyle 340m^2

\displaystyle 320m^2

\displaystyle 360m^2

\displaystyle 330m^2

Correct answer:

\displaystyle 340m^2

Explanation:

The formula for the surface area of a pyramid is:

\displaystyle SA = 4 \left(A_{triangle}\right)+Base

\displaystyle SA = 4 \left(\frac{1}{2}{h_{s}}w\right)+(lw)

Where \displaystyle h_s is the length of the slant height, \displaystyle w is the width of the base, and \displaystyle l is the length of the base

 

In order to determine the areas of the triangle, you will need to use the Pythagorean Theorem to find the slant height:

\displaystyle A^2 + B^2 = C^2

\displaystyle A^2 + (5m)^2 = (13m)^2

\displaystyle A^2 = 144m^2

\displaystyle A = 12m

 

Plugging in our values, we get:

\displaystyle SA = 4 \left(\frac{1}{2}\cdot (12m)(10m)\right)+((10m)(10m))

\displaystyle SA = 240m^2+100m^2 = 340m^2

Example Question #8 : Pyramids

Find the surface area of the following pyramid.

Pyramid

Possible Answers:

\displaystyle 316m^2

\displaystyle 336m^2

\displaystyle 356m^2

\displaystyle 326m^2

\displaystyle 346m^2

Correct answer:

\displaystyle 336m^2

Explanation:

The formula for the surface area of a pyramid is:

\displaystyle SA = (base)+\frac{1}{2}(perimeter)(slant height)

\displaystyle SA = (l)(w) + \frac{1}{2}(l+l+w+w)(h_s)

Where \displaystyle l is the length of the base, \displaystyle w is the width of the base, and \displaystyle h_s is the slant height

 

Use the Pythagorean Theorem to find the length of the slant height:

\displaystyle A^2 + B^2 = C^2

\displaystyle A^2 + (6m)^2 = (10m)^2

\displaystyle A = 8m

 

Plugging in our values, we get:

\displaystyle SA = (12m)(12m) + \frac{1}{2}(12m+12m+12m+12m)(8m)

\displaystyle SA = 336m^2

Example Question #1 : Pyramids

What is the surface area of a square pyramid with a base side equal to 4 and a slant length equal to 6?

Possible Answers:

\displaystyle 64

\displaystyle 16

\displaystyle 32

\displaystyle 48

Correct answer:

\displaystyle 64

Explanation:

The surface area of of a square pyramid can be determined using the following equation:

\displaystyle SA=2bs+b^2

\displaystyle SA=(2)(6)(4)+4^2

\displaystyle SA=48+16=64

Example Question #1 : Pyramids

What is the surface area of a square pyramid with a height of 12 in and a base side length of 10 in?

Possible Answers:

Correct answer:

Explanation:

The surface area of a square pyramid can be broken into the area of the square base and the areas of the four triangluar sides. The area of a square is given by:

\displaystyle A = s^{2} = 100 in^{2}

The area of a triangle is:

\displaystyle A = \frac{1}{2} bh

The given height of 12 in is from the vertex to the center of the base. We need to calculate the slant height of the triangular face by using the Pythagorean Theorem: 

SH^{2} = H^{2} + B^{2}\displaystyle SH^{2} = H^{2} + B^{2}

where \displaystyle H=12  and \displaystyle B= 5  (half the base side) resulting in a slant height of 13 in.

So, the area of the triangle is:

\displaystyle A = \frac{1}{2} bh = \frac{1}{2} \cdot 10 \cdot 13 = 65 in^{2}

There are four triangular sides totaling \displaystyle 260 in^{2} for the sides.

The total surface area is thus \displaystyle 360 in^{2}, including all four sides and the base.

 

Example Question #1 : Prisms

The length of a box is 3 times the width. Which of the following gives the length (L inches) in terms of the width (W inches) of the box?

Possible Answers:

L = 3W

L = W + 3

L = ½ (3W)

L = 3/W

Correct answer:

L = 3W

Explanation:

When reading word problems, there are certain clues that help interpret what is going on. The word “is” generally means “=” and the word “times” means it will be multiplied by something. Therefore, “the length of a box is 3 times the width” gives you the answer: L = 3 x W, or L = 3W.

Example Question #55 : Solid Geometry

The width of a box, in inches, is 5 inches less than three times its length. Which of the following equations gives the width, W inches, in terms of the length, L inches, of the box?

Possible Answers:

W=5L-3

W=3-5L

W=3L-5

W=5-3L

Correct answer:

W=3L-5

Explanation:

We notice the width is “5 inches less than three times its width,” so we express W as being three times its width (3L) and 5 inches less than that is 3L minus 5. In this case, W is the dependent and L is the independent variable.

W = 3L - 5

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