All PSAT Math Resources
Example Questions
Example Question #11 : X And Y Intercept
Which of the following lines does not intersect the line ?
Parallel lines never intersect, so you are looking for a line that has the same slope as the one given. The slope of the given line is –4, and the slope of the line in y = –4x + 5 is –4 as well. Since these two lines have equal slopes, they will run parallel and can never intersect.
Example Question #222 : Coordinate Geometry
Where does the line given by intercept the -axis?
First, put in slope-intercept form.
.
To find the -intercept, set and solve for .
Example Question #12 : X And Y Intercept
Find the y-intercept of .
3
7
5
14
12
7
To find the y-intercept, set x equal to zero and solve for y.
This gives y = 3(0)2 + 2(0) +7 = 7.
Example Question #173 : Geometry
The slope of a line is . The line passes through . What is the x-intercept?
None of the available answers
The equation for a line is:
, or in this case
We can solve for by plugging in the values given
Our line is now
Our x-intercept occurs when , so plugging in and solving for :
Example Question #1 : How To Find The Volume Of A Sphere
A cube with sides of 4” each contains a floating sphere with a radius of 1”. What is the volume of the space outside of the sphere, within the cube?
11.813 in3
4.187 in3
64 in3
59.813 in3
11.813 in3
59.813 in3
Volume of Cube = side3 = (4”)3 = 64 in3
Volume of Sphere = (4/3) * π * r3 = (4/3) * π * 13 = (4/3) * π * 13 = (4/3) * π = 4.187 in3
Difference = Volume of Cube – Volume of Sphere = 64 – 4.187 = 59.813 in3
Example Question #2 : How To Find The Volume Of A Sphere
If a sphere's diameter is doubled, by what factor is its volume increased?
3
4
8
2
16
8
The formula for the volume of a sphere is 4πr3/3. Because this formula is in terms of the radius, it would be easier for us to determine how the change in the radius affects the volume. Since we are told the diameter is doubled, we need to first determine how the change in the diameter affects the change in radius.
Let us call the sphere's original diameter d and its original radius r. We know that d = 2r.
Let's call the final diameter of the sphere D. Because the diameter is doubled, we know that D = 2d. We can substitute the value of d and obtain D = 2(2r) = 4r.
Let's call the final radius of the sphere R. We know that D = 2R, so we can now substituate this into the previous equation and write 2R = 4r. If we simplify this, we see that R = 2r. This means that the final radius is twice as large as the initial radius.
The initial volume of the sphere is 4πr3/3. The final volume of the sphere is 4πR3/3. Because R = 2r, we can substitute the value of R to obtain 4π(2r)3/3. When we simplify this, we get 4π(8r3)/3 = 32πr3/3.
In order to determine the factor by which the volume has increased, we need to find the ratio of the final volume to the initial volume.
32πr3/3 divided by 4πr3/3 = 8
The volume has increased by a factor of 8.
Example Question #1 : 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?
8
6
2
4
10
2
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?
16 units
8 units
2 units
4 units
128 units
128 units
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 #1 : 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?
1687.5π
4500π
3375π
None of the other answers
13500π
4500π
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 #21 : Spheres
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?
2040π√(7)
4896π
None of the other answers
4896π√(17)
816π√(11)
4896π√(17)
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 (y = 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)2 )
For our data, that is:
√( (3 + 3)2 + (24 – 0)2 ) = √( 62 + 242 ) = √(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)