SAT Math : Geometry

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #1 : How To Find The Diagonal Of A Cube

What is the length of the diagonal of a cube with volume of 512 in3?

Possible Answers:

2√(6) in

4√(3) in

8√(3) in

8 in

None of the other answers

Correct answer:

8√(3) in

Explanation:

The first thing necessary is to determine the dimensions of the cube.  This can be done using the volume formula for cubes: V = s3, where s is the length of the cube. For our data, this is:

s3 = 512, or (taking the cube root of both sides), s = 8.

The distance from corner to corner of the cube will be equal to the distance between (0,0,0) and (8,8,8).  The distance formula for three dimensions is very similar to that of 2 dimensions (and hence like the Pythagorean Theorem):

d√( (x1 – x2)2 + (y1 – y2)2  + (z1 – z2)2

Or for our simpler case:

d = √( (x)2 + (y)2  + (z)2) = √( (s)2 + (s)2  + (s)2) = √( (8)2 + (8)2  + (8)2) = √( 64 + 64 + 64) = √(64 * 3) = 8√(3)

Example Question #2 : Solid Geometry

What is the length of the diagonal of a cube with volume of 1728 in3?

Possible Answers:

12√(3) in

3√(3) in

12 in

18 in

6√(3) in

Correct answer:

12√(3) in

Explanation:

The first thing necessary is to determine the dimensions of the cube.  This can be done using the volume formula for cubes: V = s3, where s is the length of the cube. For our data, this is:

s3 = 1728, or (taking the cube root of both sides), s = 12.

The distance from corner to corner of the cube will be equal to the distance between (0,0,0) and (12,12,12).  The distance formula for three dimensions is very similar to that of 2 dimensions (and hence like the Pythagorean theorem):

d = √( (x1 – x2)2 + (y1 – y2)2  + (z1 – z2)2

Or, for our simpler case:

d = √( (x)2 + (y)2  + (z)2) = √( (s)2 + (s)2  + (s)2) = √( (12)2 + (12)2  + (12)2) = √( 144 + 144 + 144) = √(3 * 144) = 12√(3) = 12√(3)

Example Question #241 : Geometry

What is the length of the diagonal of a cube with surface area of 294 in2?

Possible Answers:

21√(2)

14

21

None of the other answers

7√(3)

Correct answer:

7√(3)

Explanation:

 The first thing necessary is to determine the dimensions of the cube. This can be done using the surface area formula for cubes: A = 6s2, where s is the length of the cube. For our data, this is:

6s2 = 294

s2 = 49

(taking the square root of both sides) s = 7

The distance from corner to corner of the cube will be equal to the distance between (0,0,0) and (7,7,7). The distance formula for three dimensions is very similar to that of 2 dimensions (and hence like the Pythagorean Theorem):

d = √((x1 – x2)2 + (y1 – y2)2  + (z1 – z2)2

Or for our simpler case:

d = √((x)2 + (y)2  + (z)2) = √( (s)2 + (s)2  + (s)2) = √( (7)2 + (7)2  + (7)2) = √( 49 + 49 + 49) =  √(49 * 3) = 7√(3)

Example Question #2 : Solid Geometry

A rectangular prism has a volume of 144 and a surface area of 192. If the shortest edge is 3, what is the length of the longest diagonal through the prism?

Possible Answers:

Correct answer:

Explanation:

The volume of a rectangular prism is .

We are told that the shortest edge is 3.  Let us call this the height. 

We now have , or .

Now we replace variables by known values:

Now we have:

We have thus determined that the other two edges of the rectangular prism will be 4 and 12.  We now need to find the longest diagonal.  This is equal to:

If you do not remember how to find this directly, you can also do it in steps.  You first find the diagonal across one of the sides (in the plane), by using the Pythagorean Theorem.  For example, we choose the side with edges 3 and 4.  This diagonal will be:

We then use a plane with one side given by the diagonal we just found (length 5) and the other given by the distance of the 3rd edge (length 12). 

This diagonal is then .

Example Question #3 : Solid Geometry

What is the surface area of a cube with a volume of 1728 in3?

Possible Answers:

432 in2

72 in2

144 in2

864 in2

1728 in2

Correct answer:

864 in2

Explanation:

This problem is relatively simple. We know that the volume of a cube is equal to s3, where s is the length of a given side of the cube. Therefore, to find our dimensions, we merely have to solve s3 = 1728. Taking the cubed root, we get s = 12.

Since the sides of a cube are all the same, the surface area of the cube is equal to 6 times the area of one face. For our dimensions, one face has an area of 12 * 12 or 144 in2. Therefore, the total surface area is 6 * 144 = 864 in2.

Example Question #1 : Cubes

A room has dimensions of 18ft by 15ft by 9ft. The last dimension is the height of the room. It has one door that is 3ft by 7ft and two windows, each 2ft by 5ft. There is no trim to the floor, wall, doors, or windows. What is the total exposed wall space?

Possible Answers:

594 ft2

1134ft2

1093ft2

553 ft2

2389ft2

Correct answer:

553 ft2

Explanation:

If broken down into parts, this is an easy problem. It is first necessary to isolate the dimensions of the walls. If the room is 9 ft high, we know 18 x 15 designates the area of the floor and ceiling. Based on this, we know that the room has the following dimensions for the walls: 18 x 9 and 15 x 9. Since there are two of each, we can calculate the total area of walls - ignoring doors and windows - by doubling the sum of these two areas:

2 * (18 * 9 + 15 * 9) = 2 * (162 + 135) = 2 * 297 = 594 ft2

Now, we merely need to calculate the area "taken out" of the walls:

For the door: 3 * 7 = 21 ft2 

For the windows: 2 * (2 * 5) = 20 ft2

The total wall space is therefore: 594 – 21 – 20 = 553 ft2

Example Question #1 : How To Find The Surface Area Of A Cube

A certain cube has a side length of 25 m.  How many square tiles, each with an area of 5 m2, are needed to fully cover the surface of the cube?

Possible Answers:

750

500

100

1000

200

Correct answer:

750

Explanation:

A cube with a side length of 25m has a surface area of:

25m * 25m * 6 = 3,750 m2

(The surface area of a cube is equal to the area of one face of the cube multiplied by 6 sides. In other words, if the side of a cube is s, then the surface area of the cube is 6s2.)

Each square tile has an area of 5 m2.

Therefore, the total number of square tiles needed to fully cover the surface of the cube is:

3,750m2/5m= 750

Note: the volume of a cube with side length s is equal to s3.  Therefore, if asked how many mini-cubes with side length n are needed to fill the original cube, the answer would be:

s3/n3

Example Question #11 : Solid Geometry

A company wants to build a cubical room around a cone so that the cone's height and diameter are 3 inch less than the dimensions of the cube. If the volume of the cone is 486π ft3, what is the surface area of the cube?

Possible Answers:

486 in2

69,984 in2

513.375 in2

726 in2

73,926 in2

Correct answer:

73,926 in2

Explanation:

To begin, we need to solve for the dimensions of the cone.

The basic form for the volume of a cone is: V = (1/3)πr2h

Using our data, we know that h = 2r because the height of the cone matches its diameter (based on the prompt).

486π  = (1/3)πr* 2r = (2/3)πr3

Multiply both sides by (3/2π): 729 = r3

Take the cube root of both sides: r = 9

Note that this is in feet. The answers are in square inches. Therefore, convert your units to inches: 9 * 12 = 108, then add 3 inches to this: 108 + 3 = 111 inches.

The surface area of the cube is defined by: A = 6 * s2, or for our data, A = 6 * 1112 = 73,926 in2

Example Question #701 : Geometry

If the volume of a cube is 216 cubic units, then what is its surface area in square units?

Possible Answers:

64

108

216

54

36

Correct answer:

216

Explanation:

The volume of a cube is given by the formula V = s^{3}, where V is the volume, and s is the length of each side. We can set V to 216 and then solve for s.

\inline 216 = s^{3}

In order to find s, we can find the cube root of both sides of the equaton. Finding the cube root of a number is the same as raising that number to the one-third power.

\sqrt[3]{216}= 216^{1/3}=6=s

This means the length of the side of the cube is 6. We can use this information to find the surface area of the cube, which is equal to \inline 6s^{2}. The formula for surface area comes from the fact that each face of the cube has an area of s^2, and there are 6 faces in a cube.

surface area = 6s^{2}=6(6^{2})=6(36)=216

The surface area of the square is 216 square units.

The answer is 216.

Example Question #702 : Geometry

You have a cube with sides of 4.5 inches. What is the surface area of the cube?

Possible Answers:

Correct answer:

Explanation:

The area of one side of the cube is:

A cube has 6 sides, so the total surface area of the cube is

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