HSPT Math : Geometry

Study concepts, example questions & explanations for HSPT Math

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Example Questions

Example Question #772 : Sat Mathematics

A rectangular prism has a length that is twice as long as its width, and a width that is twice as long as its height. If the surface area of the prism is 252 square units, what is the volume, in cubic units, of the prism?

Possible Answers:

216

27

1728

108

432

Correct answer:

216

Explanation:

Let l be the length, w be the width, and h be the height of the prism. We are told that the length is twice the width, and that the width is twice the height. We can set up the following two equations:

l = 2w

w = 2h

Next, we are told that the surface area is equal to 252 square units. Using the formula for the surface area of the rectangular prism, we can write the following equation:

surface area = 2lw + 2lh + 2wh = 252

We now have three equations and three unknowns. In order to solve for one of the variables, let's try to write w and l in terms of h. We know that w = 2h. Because l = 2w, we can write l as follows:

l = 2w = 2(2h) = 4h

Now, let's substitute w = 2h and l = 4h into the equation we wrote for surface area.

2(4h)(2h) + 2(4h)(h) + 2(2h)(h) = 252

Simplify each term.

16h2 + 8h2 + 4h2 = 252

Combine h2 terms.

28h2 = 252

Divide both sides by 28.

h2 = 9

Take the square root of both sides.

h = 3.

This means that h = 3. Because w = 2h, the width must be 6. And because l = 2w, the length must be 12.

Because we now know the length, width, and height, we can find the volume of the prism, which is what the question ultimately requires us to find.

volume of a prism = l • w • h

volume = 12(6)(3)

= 216 cubic units

The answer is 216.

Example Question #5 : Finding Volume Of A Rectangular Prism

The dimensions of Treasure Chest A are 39” x 18”. The dimensions of Treasure Chest B are  16” x 45”. Both are 11” high. Which of the following statements is correct?

Possible Answers:

Treasure Chest A has the same surface area as Treasure Chest B.

There is insufficient data to make a comparison between Treasure Chest A and Treasure Chest B.

Treasure Chest B can hold more treasure.

Treasure Chest A can hold more treasure.

Treasure Chest A and B can hold the same amount of treasure.

Correct answer:

Treasure Chest B can hold more treasure.

Explanation:

The volume of B is 7920 in3. The volume of A is 7722 in3. Treasure Chest B can hold more treasure.

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

Carlos has a pool in the shape of a rectangular prism. He fills the pool with a hose that ejects water at a rate of p gallons per minute. The bottom of the pool is A meters wide and B meters long. If there are k gallons in a cubic meter, then which of the following expressions will be equal to the amount of time it takes, in hours, for the water in the pool to reach a height of c meters?

Possible Answers:

ABcp/(60k)

ABc/(pk)

ABck/(60p)

60ABc/(pk)

60ABcp/k

Correct answer:

ABck/(60p)

Explanation:

Fillpool1

Fillpool2

Example Question #1 : Cylinders

The volume of a cylinder is 36π. If the cylinder’s height is 4, what is the cylinder’s diameter? 

Possible Answers:

12

9

6

4

3

Correct answer:

6

Explanation:

Volume of a cylinder? V = πr2h. Rewritten as a diameter equation, this is:

V = π(d/2)2h = πd2h/4

Sub in h and V: 36p = πd2(4)/4 so 36p = πd2

Thus d = 6

Example Question #2 : Cylinders

A cylinder has a height of 5 inches and a radius of 3 inches.  Find the lateral area of the cylinder.

Possible Answers:

30π

8π

15π

24π

45π

Correct answer:

30π

Explanation:

LA = 2π(r)(h) = 2π(3)(5) = 30π

Example Question #3 : Cylinders

A cylinder has a volume of 20. If the radius doubles, what is the new volume?

Possible Answers:

100

80

20

60

40

Correct answer:

80

Explanation:

The equation for the volume of the cylinder is πr2h. When the radius doubles (r becomes 2r) you get π(2r)2h = 4πr2h. So when the radius doubles, the volume quadruples, giving a new volume of 80.

Example Question #171 : Geometry

A cylinder has a height that is three times as long as its radius. If the lateral surface area of the cylinder is 54π square units, then what is its volume in cubic units?

Possible Answers:

27π

81π

243π

54π

Correct answer:

81π

Explanation:

Let us call r the radius and h the height of the cylinder. We are told that the height is three times the radius, which we can represent as h = 3r. 

We are also told that the lateral surface area is equal to 54π. The lateral surface area is the surface area that does not include the bases. The formula for the lateral surface area is equal to the circumference of the cylinder times its height, or 2πrh. We set this equal to 54π,

2πrh = 54π

Now we substitute 3r in for h.

2πr(3r) = 54π

6πr2 = 54π

Divide by 6π

r2 = 9.

Take the square root.

r = 3. 

h = 3r = 3(3) = 9.

Now that we have the radius and the height of the cylinder, we can find its volume, which is given by πr2h.

V = πr2h

V = π(3)2(9) = 81π

The answer is 81π.

Example Question #2 : Cylinders

What is the volume of a hollow cylinder whose inner radius is 2 cm and outer radius is 4 cm, with a height of 5 cm?

Possible Answers:

50π cm3

20π cm3

80π cm3

100π cm3

60π cm3

Correct answer:

60π cm3

Explanation:

The volume is found by subtracting the inner cylinder from the outer cylinder as given by V = πrout2 h – πrin2 h. The area of the cylinder using the outer radius is 80π cm3, and resulting hole is given by the volume from the inner radius, 20π cm3. The difference between the two gives the volume of the resulting hollow cylinder, 60π cm3.

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

What is the volume of a right cylinder with a circumference of 25π in and a height of 41.3 in?

Possible Answers:

3831.34π in3

25812.5π in3

6453.125π in3

4813.33π in3

1032.5π in3

Correct answer:

6453.125π in3

Explanation:

The formula for the volume of a right cylinder is: V = A * h, where A is the area of the base, or πr2.  Therefore, the total formula for the volume of the cylinder is: V = πr2h.

 First, we must solve for r by using the formula for a circumference (c = 2πr): 25π = 2πr; r = 12.5.

Based on this, we know that the volume of our cylinder must be: π*12.52*41.3 = 6453.125π in3

Example Question #6 : Cylinders

An 8-inch cube has a cylinder drilled out of it. The cylinder has a radius of 2.5 inches. To the nearest hundredth, approximately what is the remaining volume of the cube?

Possible Answers:

354.92 in3

391.33 in3

462 in3

157.08 in3

203.34 in3

Correct answer:

354.92 in3

Explanation:

We must calculate our two volumes and subtract them. The volume of the cube is very simple: 8 * 8 * 8, or 512 in3.

The volume of the cylinder is calculated by multiplying the area of its base by its height. The height of the cylinder is 8 inches (the height of the cube through which it is being drilled). Therefore, its volume is πr2h = π * 2.5* 8 = 50π in3

The volume remaining in the cube after the drilling is: 512 – 50π, or approximately 512 – 157.0795 = 354.9205, or 354.92 in3.

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