HSPT Math : Geometry

Study concepts, example questions & explanations for HSPT Math

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Example Questions

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

A sphere increases in volume by a factor of 8. By what factor does the radius change?

Possible Answers:

10

2

6

4

8

Correct answer:

2

Explanation:

Volume of a sphere is 4Πr3/3. Setting that equation equal to the original volume, the new volume is given as 8*4Πr3/3, which can be rewritten as 4Π8r3/3, and can be added to the radius value by 4Π(2r)3/3 since 8 si the cube of 2. This means the radius goes up by a factor of 2

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

A foam ball has a volume of 2 units and has a diameter of x. If a second foam ball has a radius of 2x, what is its volume?

Possible Answers:

128 units

8 units

4 units

2 units

16 units

Correct answer:

128 units

Explanation:

Careful not to mix up radius and diameter. First, we need to identify that the second ball has a radius that is 4 times as large as the first ball.  The radius of the first ball is (1/2)x and the radius of the second ball is 2x. The volume of the second ball will be 43, or 64 times bigger than the first ball.  So the second ball has a volume of 2 * 64 = 128.

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

A cross-section is made at the center of a sphere.  The area of this cross-section is 225π square units.  How many cubic units is the total volume of the sphere?

Possible Answers:

1687.5π

13500π

None of the other answers

3375π

4500π

Correct answer:

4500π

Explanation:

The solution to this is simple, though just take it step-by-step.  First find the radius of the circular cross-section.  This will give us the radius of the sphere (since this cross-section is at the center of the sphere).  If the cross-section has an area of 225π, we know its area is defined by:

A = 225π = πr2

Solving for r, we get r = 15.

From here, we merely need to use our formula for the volume of a sphere:

V = (4 / 3)πr3

For our data this is: (4 / 3)π * 153 = 4π * 152 * 5 = 4500π

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

At x = 3, the line y = 4x + 12 intersects the surface of a sphere that passes through the xy-plane. The sphere is centered at the point at which the line passes through the x-axis. What is the volume, in cubic units, of the sphere?

Possible Answers:

4896π√(17)

None of the other answers

2040π√(7)

816π√(11)

4896π

Correct answer:

4896π√(17)

Explanation:

We need to ascertain two values: The center point and the point of intersection with the surface.  Let's do that first:

The center is defined by the x-intercept. To find that, set the line equation equal to 0 (= 0 at the x-intercept):

0 = 4x + 12; 4x = –12; x = –3; Therefore, the center is at (–3,0)

Next, we need to find the point at which the line intersects with the sphere's surface. To do this, solve for the point with x-coordinate at 3:

y = 4 * 3 + 12; y = 12 + 12; y = 24; therefore, the point of intersection is at (3,24)

 

Reviewing our data so far, this means that the radius of the sphere runs from the center, (–3,0), to the edge, (3,24).  If we find the distance between these two points, we can ascertain the length of the radius.  From that, we will be able to calculate the volume of the sphere.

The distance between these two points is defined by the distance formula:

d = √( (x1 – x0)2 + (y1 – y0))

For our data, that is:

√( (3 + 3)2 + (24 – 0)) = √( 62 + 24)  = √(36 + 576) = √612 = √(2 * 2 * 3 * 3 * 17) = 6√(17)

Now, the volume of a sphere is defined by: V = (4/3)πr3

For our data, that would be:  (4/3)π * (6√(17))3 = (4/3) * 63 * 17√(17) * π = 4 * 2 * 62 * 17√(17) * π = 4896π√(17)

Example Question #6 : How To Find The Volume Of A Sphere

The surface area of a sphere is 676π in2.  How many cubic inches is the volume of the same sphere?

Possible Answers:

(2028π)/3

(8788π)/3

(2197π)/3

2028π

8788π

Correct answer:

(8788π)/3

Explanation:

To begin, we must solve for the radius of our sphere.  To do this, recall the equation for the surface area of a sphere: A = 4πr2

For our data, that is: 676π = 4πr2; 169 = r2; r = 13

From this, it is easy to solve for the volume of the sphere.  Recall the equation:

V = (4/3)πr3

For our data, this is: V = (4/3)π * 133 = (4π * 2197)/3 = (8788π)/3

Example Question #7 : How To Find The Volume Of A Sphere

What is the difference between the volume and surface area of a sphere with a radius of 6?

Possible Answers:

216π

133π

720π

288π

144π

Correct answer:

144π

Explanation:

Surface Area = 4πr2 = 4 * π * 62 = 144π

Volume = 4πr3/3 = 4 * π * 63 / 3 = 288π

Volume – Surface Area = 288π – 144π = 144π

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

A sphere is perfectly contained within a cube that has a volume of 216 units. What is the volume of the sphere?

Possible Answers:

Correct answer:

Explanation:

To begin, we must determine the dimensions of the cube. This is done by solving the simple equation:

We know the volume is 216, allowing us to solve for the length of a side of the cube.

Taking the cube root of both sides, we get s = 6.

The diameter of the sphere will be equal to side of the cube, since the question states that the sphere is perfectly contained. The diameter of the sphere will be 6, and the radius will be 3.

We can plug this into the equation for volume of a sphere:

We can cancel out the 3 in the denominator.

Simplify.

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

The surface area of a sphere is . Find the volume of the sphere in cubic millimeters.

Possible Answers:

Correct answer:

Explanation:

Example Question #111 : Solid Geometry

A solid hemisphere has a radius of length r. Let S be the number of square units, in terms of r, of the hemisphere's surface area. Let V be the number of cubic units, in terms of r, of the hemisphere's volume. What is the ratio of S to V?

Possible Answers:

\frac{9}{2r}

3r

\frac{4r}{3}

\frac{9r}{2}

\frac{3}{r}

Correct answer:

\frac{9}{2r}

Explanation:

First, let's find the surface area of the hemisphere. Because the hemisphere is basically a full sphere cut in half, we need to find half of the surface area of a full sphere. However, because the hemisphere also has a circular base, we must then add the area of the base.

S = \frac{1}{2}\cdot (surface area of sphere) + (surface area of base)

The surface area of a sphere with radius r is equal to 4\pi r^2. The surface area of the base is just equal to the surface area of a circle, which is \pi r^2.

S=\frac{1}{2}\cdot 4\pi r^2+\pi r^2=2\pi r^2+\pi r^2=3\pi r^2

The volume of the hemisphere is going to be half of the volume of an entire sphere. The volume for a full sphere is \frac{4}{3}\pi r^3.

V = \frac{1}{2}\cdot (volume of sphere)

V = \frac{1}{2}\cdot \frac{4}{3}\pi r^3=\frac{2}{3}\pi r^3

Ultimately, the question asks us to find the ratio of S to V. To do this, we can write S to V as a fraction.

\frac{S}{V}=\frac{3\pi r^2}{\frac{2}{3}\pi r^3}

In order to simplify this, let's multiply the numerator and denominator both by 3.

\frac{S}{V}=\frac{3\pi r^2}{\frac{2}{3}\pi r^3} = \frac{9\pi r^2}{2\pi r^3}=\frac{9}{2r}

The answer is \frac{9}{2r}.

Example Question #245 : Geometry

A rectangular box has a length of 2 meters, a width of 0.5 meters, and a height of 3.2 meters. How many cubes with a volume of one cubic centimeter could fit into this rectangular box?

Possible Answers:

3.2 x 102

3.2 x 10-3

3.2

3,2 x 103

3.2 x 106

Correct answer:

3.2 x 106

Explanation:

In order to figure out how many cubic centimeters can fit into the box, we need to figure out the volume of the box in terms of cubic centimeters. However, the measurements of the box are given in meters. Therefore, we need to convert these measurements to centimeters and then determine the volume of the box.

There are 100 centimeters in one meter. This means that in order to convert from meters to centimeters, we must multiply by 100.

The length of the box is 2 meters, which is equal to 2 x 100, or 200, centimeters.

The width of the box is 0.5(100) = 50 centimeters.

The height of the box is 3.2(100) = 320 centimeters.

Now that all of our measurements are in centimeters, we can calculate the volume of the box in cubic centimeters. Remember that the volume of a rectangular box (or prism) is equal to the product of the length, width, and height.

V = length x width x height

V = (200 cm)(50 cm)(320 cm) = 3,200,000 cm3

To rewrite this in scientific notation, we must move the decimal six places to the left.

V = 3.2 x 106 cm3

The answer is 3.2 x 106.

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