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Volume of pyramids, cones, and spheres

Learning goals

  • Finds volumes of pyramids, cones, and spheres from their dimensions.
  • Distinguishes perpendicular height from slant height in volume formulas.
  • Expresses volume in cubic units.
  • Finds missing dimensions from pyramid, cone, or sphere volumes.
  • Compares volumes of solids with related dimensions.

Click problems to add them to your worksheet.

Volume of pyramids, cones, and spheres 1
A sphere has radius \(3\,\text{cm}\). Find its exact volume in terms of \(\pi\).

Hints

- Identify the volume formula for a sphere. - Substitute the given radius and keep \(\pi\) exact.

Solution

1. Use \(V=\frac{4}{3}\pi r^3\): \(V=\frac{4}{3}\pi(3^3)=36\pi\,\text{cm}^3\).

Answer

The volume is \(36\pi\,\text{cm}^3\).
Volume of pyramids, cones, and spheres 2
A right circular cone has radius \(3\,\text{cm}\) and perpendicular height \(4\,\text{cm}\). Find its exact volume in terms of \(\pi\).

Hints

- Identify the volume formula for a cone. - Use the perpendicular height shown in the problem.

Solution

1. Use \(V=\frac{1}{3}\pi r^2h\): \(V=\frac{1}{3}\pi(3^2)(4)=12\pi\,\text{cm}^3\).

Answer

The volume is \(12\pi\,\text{cm}^3\).
Volume of pyramids, cones, and spheres 3
A pyramid has base area \(25\,\text{cm}^2\) and perpendicular height \(6\,\text{cm}\). Find its volume.

Hints

- The base area is already given, so no base-area calculation is needed. - Use the perpendicular height in the pyramid volume formula.

Solution

1. Use \(V=\frac{1}{3}Bh\): \(V=\frac{1}{3}(25)(6)=50\,\text{cm}^3\).

Answer

The volume is \(50\,\text{cm}^3\).
Volume of pyramids, cones, and spheres 4
Find the sphere's radius. Then write an expression for its volume without calculating it.
Figure for problem 561069

Hints

- Does the labeled segment represent a radius or a diameter? - How are the radius and diameter related? - The sphere volume formula uses the radius, not the diameter.

Solution

1. The diameter is \(8\,\text{cm}\), so the radius is half as long: \(r=4\,\text{cm}\). 2. Substitute the radius in \(V=\frac{4}{3}\pi r^3\) to get \(V=\frac{4}{3}\pi(4)^3\,\text{cm}^3\).

Answer

Radius: \(4\,\text{cm}\). Volume expression: \(\frac{4}{3}\pi(4)^3\,\text{cm}^3\).
Volume of pyramids, cones, and spheres 5
Which measurement is the pyramid's perpendicular height? Why would a sloping edge be the wrong height to use for volume?
Figure for problem 561070

Hints

- Imagine a line from the tip to the plane of the base that makes a right angle. - Which labeled length follows that line, rather than a sloping edge?

Solution

1. The perpendicular height is \(5\,\text{cm}\), measured at a right angle from the tip to the base plane. 2. A sloping edge is not the perpendicular distance, so it cannot replace the height in the volume formula.

Answer

\(5\,\text{cm}\); a sloping edge is not perpendicular to the base.
Volume of pyramids, cones, and spheres 6
The cuboid and pyramid have the same base and perpendicular height. The cuboid holds \(72\,\text{cm}^3\). What is the pyramid's volume? Explain the relationship.
Figure for problem 561071

Hints

- Compare the figures' bases and perpendicular heights, not their slanted edges. - How does the pyramid volume formula differ from the prism formula?

Solution

1. The volume of a pyramid with the same base area and perpendicular height is one-third the volume of the matching prism. 2. Its volume is \(72\div3=24\,\text{cm}^3\).

Answer

\(24\,\text{cm}^3\), one-third of the cuboid's volume.
Volume of pyramids, cones, and spheres 7
A cone-shaped glass has the dimensions shown. Find its maximum volume. Give the exact value in terms of \(\pi\), then round to the nearest tenth.
Figure for problem 531568

Hints

- Read the radius and height from the diagram. - Use the cone volume formula. - Write the exact answer with \(\pi\) before calculating a decimal approximation. - Round only in the final step.

Solution

1. The diagram shows radius \(r=5\,\text{cm}\) and height \(h=12\,\text{cm}\). 2. Use \(V=\frac{1}{3}\pi r^2h\): \(V=\frac{1}{3}\pi\cdot5^2\cdot12=100\pi\,\text{cm}^3\). 3. Numerically, \(100\pi\approx314.2\,\text{cm}^3\).

Answer

Exact value: \(100\pi\,\text{cm}^3\) Rounded value: \(314.2\,\text{cm}^3\)
Volume of pyramids, cones, and spheres 8
A wooden sphere has the radius shown. Find its volume. Give the exact value in terms of \(\pi\), then round to the nearest tenth.
Figure for problem 531569

Hints

- Determine whether the labeled measurement is a radius or diameter. - Use the sphere volume formula. - Simplify the exact expression before finding a decimal approximation. - Round only the decimal value.

Solution

1. The diagram shows radius \(r=6\,\text{cm}\). 2. Use \(V=\frac{4}{3}\pi r^3\): \(V=\frac{4}{3}\pi\cdot6^3=288\pi\,\text{cm}^3\). 3. Numerically, \(288\pi\approx904.8\,\text{cm}^3\).

Answer

Exact value: \(288\pi\,\text{cm}^3\) Rounded value: \(904.8\,\text{cm}^3\)
Volume of pyramids, cones, and spheres 9
A paper cup is shaped like a cone with radius \(4\,\text{cm}\) and height \(9\,\text{cm}\). Find its maximum capacity in milliliters and round to the nearest tenth. Use \(1\,\text{cm}^3=1\,\text{mL}\).

Hints

- Identify the solid as a cone. - Use the radius and height in the cone volume formula. - Convert cubic centimeters to milliliters using the given equivalence. - Round only the final value.

Solution

1. Use the cone volume formula: \(V=\frac{1}{3}\pi r^2h\). 2. Substitute the measurements: \(V=\frac{1}{3}\pi\cdot4^2\cdot9=48\pi\,\text{cm}^3\). 3. Since \(48\pi\approx150.7964\), the capacity is approximately \(150.8\,\text{mL}\).

Answer

The maximum capacity is approximately \(150.8\,\text{mL}\).
Volume of pyramids, cones, and spheres 10
A cone-shaped container is \(12\,\text{cm}\) deep and has a top diameter of \(5\,\text{cm}\). What is its volume when filled to the rim? Round to the nearest tenth.

Hints

- Determine whether the given circular measurement is a radius or a diameter. - Convert the diameter to a radius. - Substitute the radius and height into the cone volume formula.

Solution

1. The radius is half the diameter: \(r=5\div2=2.5\,\text{cm}\). 2. Use the cone volume formula: \(V=\frac{1}{3}\pi r^2h\). 3. Substitute: \(V=\frac{1}{3}\pi\cdot2.5^2\cdot12=25\pi\,\text{cm}^3\). 4. Since \(25\pi\approx78.5398\), the volume is approximately \(78.5\,\text{cm}^3\).

Answer

The container volume is approximately \(78.5\,\text{cm}^3\).
Volume of pyramids, cones, and spheres 11
A conical pile of road sand has a base radius of \(7\,\text{m}\) and a height of \(12\,\text{m}\). Find its volume and round to the nearest tenth.

Hints

- Use the cone volume formula. - Compare the cone formula with the cylinder formula for the same base and height.

Solution

1. Use \(V=\frac{1}{3}\pi r^2h\). 2. Substitute: \(V=\frac{1}{3}\pi\cdot7^2\cdot12=196\pi\,\text{m}^3\). 3. Since \(196\pi\approx615.7522\), the volume is approximately \(615.8\,\text{m}^3\).

Answer

The sand pile volume is approximately \(615.8\,\text{m}^3\).
Volume of pyramids, cones, and spheres 12
A monument is shaped like a square pyramid with base edge length \(12\,\text{m}\) and height \(9\,\text{m}\). Find its volume.

Hints

- Find the area of the square base first. - A pyramid has one-third the volume of a prism with the same base and height.

Solution

1. The square base area is \(B=12^2=144\,\text{m}^2\). 2. The pyramid volume is \(V=\frac{1}{3}Bh=\frac{1}{3}\cdot144\cdot9=432\,\text{m}^3\).

Answer

The monument volume is \(432\,\text{m}^3\).
Volume of pyramids, cones, and spheres 13
Find the sphere's exact volume and its volume rounded to the nearest tenth of a cubic centimeter.
Figure for problem 555589

Hints

- Identify whether the pictured measurement runs across the whole sphere. - The formula takes a radius, not a diameter. - Keep \(\pi\) until the final rounding step.

Solution

1. The displayed diameter is \(12\,\text{cm}\), so the radius is \(r=6\,\text{cm}\). 2. Use the sphere-volume formula: \(V=\frac{4}{3}\pi r^3=\frac{4}{3}\pi(6)^3=288\pi\,\text{cm}^3\). 3. Therefore, \(V\approx904.8\,\text{cm}^3\) to the nearest tenth.

Answer

\(V=288\pi\,\text{cm}^3\approx904.8\,\text{cm}^3\)
Volume of pyramids, cones, and spheres 14
A triangular pyramid has a right-triangular base whose perpendicular legs are \(8\,\text{cm}\) and \(15\,\text{cm}\). The pyramid's perpendicular height is \(9\,\text{cm}\). Find its volume.

Hints

- Find the area of the triangular base before using the solid's height. - Distinguish the dimensions inside the base triangle from the perpendicular height of the pyramid. - Check that the final unit is cubic centimeters.

Solution

1. The base area is \(B=\frac{1}{2}(8)(15)=60\,\text{cm}^2\). 2. The volume of a pyramid is \(V=\frac{1}{3}Bh\). 3. Thus, \(V=\frac{1}{3}(60)(9)=180\,\text{cm}^3\).

Answer

\(180\,\text{cm}^3\)
Volume of pyramids, cones, and spheres 15
How many times as great is pyramid b)'s volume as pyramid a)'s volume? Explain using their base areas and heights.
Figure for problem 561072

Hints

- Compare the base areas first. - The heights stay fixed. What does that mean for the volume ratio? - A doubled length does not mean a doubled square area.

Solution

1. Doubling both sides of the square base multiplies its area by \(2^2=4\). 2. Both pyramids have the same height and the same one-third factor. 3. Therefore the larger pyramid has four times the smaller pyramid's volume.

Answer

\(4\) times as great.
Volume of pyramids, cones, and spheres 16
What fraction of cylinder b)'s volume is cone a)'s volume? Find each exact volume.
Figure for problem 561073

Hints

- What does each solid's circular base contribute to volume? - Compare the labeled radii and perpendicular heights. - Which two volume formulas apply?

Solution

1. Both have base area \(\pi(2)^2=4\pi\,\text{cm}^2\). 2. The cylinder volume is \(4\pi\cdot6=24\pi\,\text{cm}^3\). 3. The cone volume is \(\frac{1}{3}\cdot24\pi=8\pi\,\text{cm}^3\).

Answer

The cone occupies \(\frac{1}{3}\) of the cylinder volume. Cone: \(8\pi\,\text{cm}^3\); cylinder: \(24\pi\,\text{cm}^3\).
Volume of pyramids, cones, and spheres 17
A right circular cone has the dimensions shown. Its slant height is \(5\,\text{cm}\). Explain why using \(5\) as the height in the volume formula is wrong. Then find its exact volume.
Figure for problem 561074

Hints

- Find the distance that is perpendicular to the base plane. - Where does the slant height lie compared with the vertical segment? - Check that you use the radius for the circular base.

Solution

1. Volume uses the perpendicular distance from the tip to the base, which is \(4\,\text{cm}\), not the slant height along the side. 2. The base radius is \(3\,\text{cm}\). 3. Thus \(V=\frac{1}{3}\pi(3)^2(4)=12\pi\,\text{cm}^3\).

Answer

The perpendicular height is \(4\,\text{cm}\); the slant height does not belong in the volume formula. \(V=12\pi\,\text{cm}^3\).
Volume of pyramids, cones, and spheres 18
Find the exact volume of the sphere.
Figure for problem 561075

Hints

- Is the marked length a radius or a diameter? - How would you find the distance from the sphere's center to its surface? - Check which length belongs in the sphere-volume formula.

Solution

1. The diameter is \(6\,\text{cm}\), so \(r=3\,\text{cm}\). 2. Use \(V=\frac{4}{3}\pi r^3=\frac{4}{3}\pi(3)^3=36\pi\,\text{cm}^3\).

Answer

\(36\pi\,\text{cm}^3\)
Volume of pyramids, cones, and spheres 19
A balloon is spherical. Its radius changes from \(2\,\text{in}\) to \(6\,\text{in}\). By what factor does its volume change? Explain without calculating either exact volume.

Hints

- Which part of the sphere volume formula changes? - A length factor affects volume in three dimensions. - Compare the two cubes of the radius as a ratio.

Solution

1. The new radius is three times the old radius. 2. Sphere volume is proportional to the cube of its radius. 3. The new volume is \(3^3=27\) times the old volume.

Answer

The volume becomes \(27\) times as great.
Volume of pyramids, cones, and spheres 20
A right circular cone has radius \(3\,\text{cm}\) and volume \(18\pi\,\text{cm}^3\). Find its perpendicular height.

Hints

- Start with the cone volume formula, leaving height unknown. - Cancel a factor common to both sides of your equation. - Check the recovered height by substituting it back.

Solution

1. Use \(V=\frac{1}{3}\pi r^2h\). 2. Substituting the known values gives \(18\pi=\frac{1}{3}\pi(3)^2h=3\pi h\). 3. Divide by \(3\pi\): \(h=6\,\text{cm}\).

Answer

\(6\,\text{cm}\)
Volume of pyramids, cones, and spheres 21
Three modeling-clay spheres have radii \(1\,\text{cm}\), \(6\,\text{cm}\), and \(8\,\text{cm}\). They are combined and reshaped into one sphere. What is the radius of the new sphere?

Hints

- The total amount of clay, and therefore the total volume, stays the same. - Write the sphere volume formula for each original sphere. - Factor out the common constants before solving for the new radius.

Solution

1. Volume is conserved. The total volume is \(\frac{4}{3}\pi\left(1^3+6^3+8^3\right)\). 2. The sum of the cubes is \(1+216+512=729\). 3. If \(R\) is the new radius, then \(\frac{4}{3}\pi R^3=\frac{4}{3}\pi\cdot729\). 4. Therefore, \(R^3=729\), so \(R=\sqrt[3]{729}=9\,\text{cm}\).

Answer

The new sphere has radius \(9\,\text{cm}\).
Volume of pyramids, cones, and spheres 22
A spherical weather balloon has volume \(V=14.5\,\text{m}^3\). 1. Find its radius \(r\) in meters. Round to the nearest hundredth. 2. Find its surface area \(SA\) in square meters. Round to the nearest hundredth. Use \(V=\frac{4}{3}\pi r^3\) and \(SA=4\pi r^2\). Keep full precision until each final rounding.

Hints

- Isolate \(r^3\) in the volume formula, then take a cube root. - Keep the calculator value of the radius available for the surface-area calculation instead of reusing the rounded radius. - Check that the first answer has length units and the second has square units.

Solution

1. Solve the volume formula for the radius: \(r=\sqrt[3]{\frac{3V}{4\pi}}\). Thus \(r=\sqrt[3]{\frac{3\cdot14.5}{4\pi}}\approx1.51\,\text{m}\). 2. Use the unrounded radius in the surface-area formula: \(SA=4\pi\left(\sqrt[3]{\frac{3\cdot14.5}{4\pi}}\right)^2\approx28.76\,\text{m}^2\).

Answer

1. \(r\approx1.51\,\text{m}\) 2. \(SA\approx28.76\,\text{m}^2\)
Volume of pyramids, cones, and spheres 23
A wooden sphere has surface area \(SA=800\,\text{cm}^2\). First find its radius \(r\), and then find its volume \(V\). Round each final answer to the nearest hundredth, keeping full precision between calculations.

Hints

- Rearrange the sphere surface-area formula to isolate the radius. - Keep the calculator value of the radius for the volume calculation rather than reusing the rounded radius. - Check that radius uses linear units and volume uses cubic units.

Solution

1. From \(SA=4\pi r^2\), \(r=\sqrt{\frac{800}{4\pi}}\approx7.98\,\text{cm}\). 2. Use the unrounded radius in the volume formula: \(V=\frac{4}{3}\pi\left(\sqrt{\frac{800}{4\pi}}\right)^3\approx2127.69\,\text{cm}^3\).

Answer

\(r\approx7.98\,\text{cm}\) \(V\approx2127.69\,\text{cm}^3\)
Volume of pyramids, cones, and spheres 24
A punch bowl is shaped like a hemisphere and holds exactly \(4\,\text{L}\) when filled to the rim. Find the interior diameter in centimeters and round to the nearest tenth.

Hints

- Convert liters to cubic centimeters. - A hemisphere has half the volume of a sphere. - Rearrange the volume formula to solve for the radius. - Double the radius because the problem asks for diameter.

Solution

1. Convert the capacity: \(4\,\text{L}=4{,}000\,\text{cm}^3\). 2. A hemisphere has volume \(V=\frac{2}{3}\pi r^3\). 3. Solve for the radius: \(r=\sqrt[3]{\frac{3V}{2\pi}}=\sqrt[3]{\frac{3\cdot4{,}000}{2\pi}}\approx12.4070\,\text{cm}\). 4. The diameter is \(d=2r\approx24.8140\,\text{cm}\), which rounds to \(24.8\,\text{cm}\).

Answer

The interior diameter is approximately \(24.8\,\text{cm}\).
Volume of pyramids, cones, and spheres 25
A spherical chocolate has diameter \(3\,\text{cm}\). A special edition is made as a hemisphere with twice the diameter, \(6\,\text{cm}\). How many times as great is the new hemisphere's volume as the original sphere's volume?

Hints

- Find the volume of each solid and compare them. - Volume changes by the cube of a linear scale factor. - A hemisphere has half the volume of a sphere with the same radius. - Divide the new volume by the original volume.

Solution

1. The original sphere has radius \(1.5\,\text{cm}\), so its volume is \(V_1=\frac{4}{3}\pi\cdot1.5^3=4.5\pi\,\text{cm}^3\). 2. The new hemisphere has radius \(3\,\text{cm}\), so its volume is \(V_2=\frac{2}{3}\pi\cdot3^3=18\pi\,\text{cm}^3\). 3. The volume factor is \(\frac{V_2}{V_1}=\frac{18\pi}{4.5\pi}=4\). 4. Equivalently, doubling all linear dimensions multiplies a sphere's volume by \(2^3=8\), and taking half of that sphere gives a factor of \(4\).

Answer

The new hemisphere has \(4\) times the volume of the original sphere.
Volume of pyramids, cones, and spheres 26
A spherical container has a capacity of \(12\,\text{L}\). a) Find the radius \(r\) in decimeters. b) Find the surface area \(SA\) in square decimeters. Round each answer to the nearest hundredth. Use \(1\,\text{L}=1\,\text{dm}^3\).

Hints

- Convert liters to cubic decimeters. - Rearrange the sphere volume formula and take a cube root. - Use the calculated radius in the sphere surface-area formula. - Keep the unrounded radius for the second calculation.

Solution

1. The volume is \(12\,\text{dm}^3\). 2. Solve \(V=\frac{4}{3}\pi r^3\) for the radius: \(r=\sqrt[3]{\frac{3V}{4\pi}}=\sqrt[3]{\frac{36}{4\pi}}=\sqrt[3]{\frac{9}{\pi}}\approx1.420248\,\text{dm}\). 3. Therefore, \(r\approx1.42\,\text{dm}\). 4. Using the unrounded radius, \(SA=4\pi r^2\approx25.3477\,\text{dm}^2\), so \(SA\approx25.35\,\text{dm}^2\).

Answer

a) \(r\approx1.42\,\text{dm}\) b) \(SA\approx25.35\,\text{dm}^2\)
Volume of pyramids, cones, and spheres 27
A square pyramid has a base edge length of \(12\,\text{cm}\) and a height of \(18\,\text{cm}\). It is cut halfway up its height by a plane parallel to the base, and the small pyramid above the cut is removed. Find the volume of the remaining frustum.

Hints

- Use similarity to determine the small pyramid's base edge. - The cut divides the original height into two equal parts. - Find the volume of the original pyramid and subtract the volume of the smaller pyramid.

Solution

1. The cut is halfway up the original height, so the small removed pyramid has height \(9\,\text{cm}\) and linear scale factor \(\frac{1}{2}\). 2. Its base edge is \(\frac{1}{2}\cdot12=6\,\text{cm}\). 3. The original pyramid volume is \(V_L=\frac{1}{3}\cdot12^2\cdot18=864\,\text{cm}^3\). 4. The small pyramid volume is \(V_s=\frac{1}{3}\cdot6^2\cdot9=108\,\text{cm}^3\). 5. The frustum volume is \(864-108=756\,\text{cm}^3\).

Answer

The frustum volume is \(756\,\text{cm}^3\).
Volume of pyramids, cones, and spheres 28
Find the volume of the rectangular-pyramid frustum shown. Explain how the two rectangular bases help you work out the heights of the full pyramid and the small pyramid removed from its tip.
Figure for problem 528689

Hints

- Compare corresponding edges of the two rectangular bases. - Imagine extending the sloping edges until they meet at a tip. - How do the base-side ratios compare with the heights of the two similar pyramids? - Subtract the smaller pyramid's volume from the full pyramid's volume.

Solution

1. The corresponding side-length ratios are \(5.0\div12.5=3.2\div8.0=0.4\), so the removed pyramid has a length scale factor of \(0.4\). 2. Let \(H\) be the full pyramid height. The removed pyramid's height is \(0.4H\), so \(H-0.4H=9.0\). Thus \(H=15\,\text{cm}\) and the removed height is \(6\,\text{cm}\). 3. The lower and upper base areas are \(12.5\cdot8.0=100\,\text{cm}^2\) and \(5.0\cdot3.2=16\,\text{cm}^2\). 4. Subtract the pyramid volumes: \(V=\frac{1}{3}\cdot100\cdot15-\frac{1}{3}\cdot16\cdot6=468\,\text{cm}^3\).

Answer

\(468\,\text{cm}^3\)
Volume of pyramids, cones, and spheres 29
Find the volume of a rectangular-pyramid frustum with the following dimensions. Give the result in cubic meters. Lower base: \(2.40\,\text{m}\times1.50\,\text{m}\) Upper base: \(80\,\text{cm}\times50\,\text{cm}\) Frustum height: \(1.80\,\text{m}\)

Hints

- Convert all lengths to meters first. - Check the similarity ratio between the two rectangular bases. - Express the frustum as the difference of two similar pyramids. - Keep track of square and cubic units.

Solution

1. Convert the upper base dimensions: \(80\,\text{cm}=0.80\,\text{m}\) and \(50\,\text{cm}=0.50\,\text{m}\). 2. The upper base dimensions are one-third of the corresponding lower base dimensions. If the full pyramid height is \(H\), the removed pyramid height is \(\frac{H}{3}\). 3. The frustum height is \(H-\frac{H}{3}=\frac{2H}{3}=1.80\), so \(H=2.70\,\text{m}\), and the removed height is \(0.90\,\text{m}\). 4. The lower and upper base areas are \(2.40\cdot1.50=3.60\,\text{m}^2\) and \(0.80\cdot0.50=0.40\,\text{m}^2\). 5. Therefore, \(V=\frac{1}{3}\cdot3.60\cdot2.70-\frac{1}{3}\cdot0.40\cdot0.90=3.24-0.12=3.12\,\text{m}^3\).

Answer

\(V=3.12\,\text{m}^3\)
Volume of pyramids, cones, and spheres 30
A stone planter is shaped like an inverted square-pyramid frustum. The square bottom has side length \(40\,\text{cm}\), the square opening has side length \(60\,\text{cm}\), and the interior height is \(45\,\text{cm}\). How many liters of soil are needed to fill the planter to the top?

Hints

- Compare the side lengths of the top and bottom squares. - Extend the sides to create two similar pyramids sharing an apex. - Use the similarity ratio to determine the two pyramid heights. - Convert the final cubic-centimeter volume to liters.

Solution

1. The opening side is \(1.5\) times the bottom side. Extend the slanted sides downward to a common apex below the planter. 2. Let \(x\) be the height from the apex to the smaller bottom square. Then \(\frac{x+45}{x}=1.5\), so \(x=90\,\text{cm}\). The larger pyramid height is \(135\,\text{cm}\). 3. The large and small square base areas are \(60^2=3{,}600\,\text{cm}^2\) and \(40^2=1{,}600\,\text{cm}^2\). 4. The planter volume is \(V=\frac{1}{3}\cdot3{,}600\cdot135-\frac{1}{3}\cdot1{,}600\cdot90=162{,}000-48{,}000=114{,}000\,\text{cm}^3\). 5. Since \(1{,}000\,\text{cm}^3=1\,\text{L}\), the planter holds \(114\,\text{L}\).

Answer

The planter requires \(114\,\text{L}\) of soil.
Volume of pyramids, cones, and spheres 31
A concrete footing for a heavy metal post is shaped like a rectangular-pyramid frustum. The lower base measures \(120\,\text{cm}\times80\,\text{cm}\), the upper base measures \(60\,\text{cm}\times40\,\text{cm}\), and the vertical height is \(50\,\text{cm}\). Find the concrete volume in cubic meters.

Hints

- Compare corresponding dimensions of the two rectangular bases. - Model the frustum as a large pyramid minus a smaller similar pyramid. - Use the scale factor to determine the full and removed pyramid heights. - Convert cubic centimeters to cubic meters only after finding the volume.

Solution

1. Each upper-base dimension is half the corresponding lower-base dimension, so the removed top pyramid has scale factor \(\frac{1}{2}\) relative to the full pyramid. 2. Let \(H\) be the full pyramid height. The removed pyramid height is \(\frac{H}{2}\), and the frustum height is also \(\frac{H}{2}=50\). Thus, \(H=100\,\text{cm}\). 3. The lower and upper base areas are \(120\cdot80=9{,}600\,\text{cm}^2\) and \(60\cdot40=2{,}400\,\text{cm}^2\). 4. The frustum volume is \(V=\frac{1}{3}\cdot9{,}600\cdot100-\frac{1}{3}\cdot2{,}400\cdot50=320{,}000-40{,}000=280{,}000\,\text{cm}^3\). 5. Since \(1\,\text{m}^3=1{,}000{,}000\,\text{cm}^3\), \(V=0.28\,\text{m}^3\).

Answer

The required concrete volume is \(0.28\,\text{m}^3\).
Volume of pyramids, cones, and spheres 32
A cleaning bucket is shaped like a cone frustum. It is \(28\,\text{cm}\) tall, the top diameter is \(32\,\text{cm}\), and the bottom diameter is \(24\,\text{cm}\). Find its capacity in liters and round to the nearest tenth.

Hints

- Convert the diameters to radii. - Extend the sides to model the frustum as the difference of two similar cones. - Use the radius ratio to determine the two cone heights. - Convert cubic centimeters to liters at the end.

Solution

1. The top and bottom radii are \(16\,\text{cm}\) and \(12\,\text{cm}\). 2. Extend the slanted sides below the bucket to form two similar cones. Let \(x\) be the height of the smaller cone. Since the radius ratio is \(16\div12=\frac{4}{3}\), \(\frac{x+28}{x}=\frac{4}{3}\), so \(x=84\,\text{cm}\). The larger cone height is \(112\,\text{cm}\). 3. The bucket volume is the difference of the two cone volumes: \(V=\frac{1}{3}\pi\cdot16^2\cdot112-\frac{1}{3}\pi\cdot12^2\cdot84=\frac{16{,}576\pi}{3}\approx17{,}358.35\,\text{cm}^3\). 4. Since \(1{,}000\,\text{cm}^3=1\,\text{L}\), the capacity is approximately \(17.358\,\text{L}\), or \(17.4\,\text{L}\) to the nearest tenth.

Answer

The bucket capacity is approximately \(17.4\,\text{L}\).
Volume of pyramids, cones, and spheres 33
A glass paperweight is shaped like a right square-pyramid frustum. The lower base edge is \(10\,\text{cm}\), the upper base edge is \(5\,\text{cm}\), and the frustum height is \(6\,\text{cm}\). Find its volume.

Hints

- Compare the two square edge lengths. - Extend the lateral edges to form the original full pyramid. - Use the similarity ratio to relate the full and removed pyramid heights. - Subtract the smaller pyramid volume from the larger one.

Solution

1. The upper base edge is half the lower base edge, so the small removed pyramid is a \(\frac{1}{2}\)-scale copy of the full pyramid. 2. If the full pyramid height is \(H\), the small pyramid height is \(\frac{H}{2}\). The frustum height is \(H-\frac{H}{2}=6\), so \(H=12\,\text{cm}\), and the small pyramid height is \(6\,\text{cm}\). 3. The lower and upper base areas are \(100\,\text{cm}^2\) and \(25\,\text{cm}^2\). 4. Subtract the small pyramid volume from the full pyramid volume: \(V=\frac{1}{3}\cdot100\cdot12-\frac{1}{3}\cdot25\cdot6=400-50=350\,\text{cm}^3\).

Answer

The paperweight volume is \(350\,\text{cm}^3\).
Volume of pyramids, cones, and spheres 34
A square pyramid has a base edge length of \(6\,\text{cm}\) and a height of \(9\,\text{cm}\). A plane parallel to the base cuts the pyramid \(3\,\text{cm}\) above the base. a) What shape is the cross section? b) Find the volume of the lower solid, which is a pyramid frustum.

Hints

- A cross section parallel to a pyramid's base has the same shape as the base. - Find the lower volume by subtracting the small top pyramid from the original pyramid. - Use similarity to determine the cross-section edge length.

Solution

1. A plane parallel to a square pyramid's base creates a square cross section. 2. The original pyramid volume is \(V_L=\frac{1}{3}\cdot6^2\cdot9=108\,\text{cm}^3\). 3. The small pyramid above the cut has height \(9-3=6\,\text{cm}\), so its linear scale factor is \(6\div9=\frac{2}{3}\). Its base edge is \(\frac{2}{3}\cdot6=4\,\text{cm}\), and its volume is \(V_s=\frac{1}{3}\cdot4^2\cdot6=32\,\text{cm}^3\). 4. Therefore, the frustum volume is \(108-32=76\,\text{cm}^3\).

Answer

a) The cross section is a square. b) The frustum volume is \(76\,\text{cm}^3\).
Volume of pyramids, cones, and spheres 35
A sphere with diameter \(12\,\text{cm}\) fits exactly inside a cube with side length \(12\,\text{cm}\). Find the sphere's volume. What percent of the cube's volume does the sphere occupy? Round the percent to the nearest tenth.

Hints

- Find the volume of each solid separately. - The sphere's diameter equals the cube's side length. - Divide the sphere's volume by the cube's volume and convert to a percent.

Solution

1. The sphere has radius \(6\,\text{cm}\), so \(V_s=\frac{4}{3}\pi\cdot6^3=288\pi\,\text{cm}^3\approx904.78\,\text{cm}^3\). 2. The cube's volume is \(V_c=12^3=1728\,\text{cm}^3\). 3. The percentage is \(\frac{288\pi}{1728}\cdot100\%=\frac{\pi}{6}\cdot100\%\approx52.4\%\).

Answer

Sphere volume: \(288\pi\,\text{cm}^3\approx904.78\,\text{cm}^3\) Percent of cube volume: approximately \(52.4\%\)
Volume of pyramids, cones, and spheres 36
A baking pan is shaped like a shallow rectangular-pyramid frustum. The bottom measures \(24\,\text{cm}\times18\,\text{cm}\), the top opening measures \(32\,\text{cm}\times24\,\text{cm}\), and the depth is \(5\,\text{cm}\). Find the pan's capacity in cubic centimeters.

Hints

- Compare corresponding top and bottom dimensions. - Extend the sides to model the pan as the difference of two similar pyramids. - Use the scale factor and the known depth to find the two pyramid heights. - Subtract the smaller pyramid volume from the larger one.

Solution

1. The top dimensions are \(\frac{4}{3}\) times the corresponding bottom dimensions. Extend the slanted sides below the pan to form two similar pyramids. 2. Let \(x\) be the height from the common apex to the smaller bottom rectangle. Then \(\frac{x+5}{x}=\frac{4}{3}\), so \(x=15\,\text{cm}\). The larger pyramid height is \(20\,\text{cm}\). 3. The top and bottom areas are \(32\cdot24=768\,\text{cm}^2\) and \(24\cdot18=432\,\text{cm}^2\). 4. The capacity is \(V=\frac{1}{3}\cdot768\cdot20-\frac{1}{3}\cdot432\cdot15=5120-2160=2960\,\text{cm}^3\).

Answer

The baking pan has a capacity of \(2960\,\text{cm}^3\).
Volume of pyramids, cones, and spheres 37
Find the volume of the square-pyramid frustum shown. Explain how to extend its sides to form a complete pyramid and then subtract the smaller pyramid cut from its tip.
Figure for problem 536056

Hints

- Imagine extending the sloping edges until they meet at one tip. - Compare the upper and lower square edges to find the scale factor for the removed pyramid. - Express the two pyramid heights using the frustum's perpendicular height. - Subtract the top pyramid's volume from the complete pyramid's volume.

Solution

1. The lower square edge is \(12\,\text{cm}\), the upper edge is \(4\,\text{cm}\), and the perpendicular frustum height is \(9\,\text{cm}\). 2. The upper edge is one-third the lower edge, so the small removed pyramid has height \(\frac{H}{3}\) if the complete pyramid has height \(H\). 3. The frustum height is \(H-\frac{H}{3}=\frac{2H}{3}=9\), giving \(H=13.5\,\text{cm}\) and a removed height of \(4.5\,\text{cm}\). 4. The complete pyramid has volume \(\frac{1}{3}\cdot12^2\cdot13.5=648\,\text{cm}^3\). 5. The small pyramid has volume \(\frac{1}{3}\cdot4^2\cdot4.5=24\,\text{cm}^3\). 6. Subtracting gives \(648-24=624\,\text{cm}^3\).

Answer

\(624\,\text{cm}^3\)
Volume of pyramids, cones, and spheres 38
A small glass solid is shaped like a right square-pyramid frustum. Its lower base edge is \(5\,\text{cm}\), its upper base edge is \(3\,\text{cm}\), and its height is \(4.5\,\text{cm}\). Find its volume.

Hints

- Use the ratio of the upper and lower base edges as a similarity scale factor. - Relate the full pyramid height, removed pyramid height, and frustum height. - Find the two pyramid volumes before subtracting.

Solution

1. The linear scale factor from the full pyramid to the removed pyramid is \(3\div5=0.6\). 2. If the full pyramid height is \(H\), the removed height is \(0.6H\). Therefore, \(H-0.6H=0.4H=4.5\), so \(H=11.25\,\text{cm}\), and the removed height is \(6.75\,\text{cm}\). 3. The full pyramid volume is \(\frac{1}{3}\cdot5^2\cdot11.25=93.75\,\text{cm}^3\). 4. The removed pyramid volume is \(\frac{1}{3}\cdot3^2\cdot6.75=20.25\,\text{cm}^3\). 5. The frustum volume is \(93.75-20.25=73.5\,\text{cm}^3\).

Answer

The glass solid has volume \(73.5\,\text{cm}^3\).
Volume of pyramids, cones, and spheres 39
A right circular cone has radius \(6\,\text{cm}\) and slant height \(\ell=10\,\text{cm}\). Find the cone's exact volume.

Hints

- The volume formula needs the perpendicular height rather than the slant height. - Use the right triangle formed by the radius, perpendicular height, and slant height. - Keep \(\pi\) symbolic because an exact volume is requested.

Solution

1. In an axial right triangle, the radius, perpendicular height, and slant height satisfy \(6^2+h^2=10^2\). 2. Thus, \(h^2=64\), so \(h=8\,\text{cm}\). 3. The cone's volume is \(V=\frac{1}{3}\pi r^2h=\frac{1}{3}\pi(6^2)(8)=96\pi\,\text{cm}^3\).

Answer

\(96\pi\,\text{cm}^3\)
Volume of pyramids, cones, and spheres 40
A square pyramid has volume \(588\,\text{cm}^3\) and perpendicular height \(9\,\text{cm}\). Find the side length of its square base.

Hints

- Work backward from the pyramid-volume formula to the base area. - Express the area of a square base in terms of one side length. - A geometric length must be positive.

Solution

1. Let the base side length be \(x\), so the base area is \(B=x^2\). 2. From \(V=\frac{1}{3}Bh\), \(588=\frac{1}{3}x^2(9)=3x^2\). 3. Therefore, \(x^2=196\), and the positive length is \(x=14\,\text{cm}\).

Answer

\(14\,\text{cm}\)
Volume of pyramids, cones, and spheres 41
Sphere B has exactly six times the volume of sphere A. By what multiplicative factor \(k\) is the diameter of sphere B scaled from the diameter of sphere A? Give an exact radical expression and a decimal approximation to the nearest hundredth.

Hints

- Write the sphere volume formula for both spheres and form a ratio. - Cancel constants that are common to both volumes. - A volume scale factor corresponds to the cube of the linear scale factor. - Radius and diameter have the same scale factor.

Solution

1. The volume relationship is \(V_B=6V_A\). 2. Using \(V=\frac{4}{3}\pi r^3\), \(\frac{4}{3}\pi r_B^3=6\left(\frac{4}{3}\pi r_A^3\right)\). 3. Cancel the common factor to get \(r_B^3=6r_A^3\). 4. Take cube roots: \(r_B=\sqrt[3]{6}\,r_A\). 5. Diameter is proportional to radius, so \(k=\frac{d_B}{d_A}=\sqrt[3]{6}\approx1.82\).

Answer

\(k=\sqrt[3]{6}\approx1.82\)
Volume of pyramids, cones, and spheres 42
The concrete planter shown is shaped like an inverted rectangular-pyramid frustum. Its inside measurements are marked. How many liters of soil can it hold when filled to the top?
Figure for problem 528681

Hints

- Compare the two rectangular end faces; corresponding lengths have the same ratio. - Extend the sloping sides in your mind to make a complete pyramid below the planter. - Similar pyramids give a relationship between the two distances from their shared tip. - Subtract the smaller pyramid's volume, then convert cubic centimeters to liters.

Solution

1. The upper rectangle is a scale copy of the lower rectangle, with scale factor \(\frac{60}{40}=\frac{45}{30}=1.5\). 2. Extend the sloping sides downward to complete a larger pyramid. Let \(x\) be the height from the common tip to the lower base. Then \(\frac{x+50}{x}=1.5\), so \(x=100\,\text{cm}\) and the complete height is \(150\,\text{cm}\). 3. The larger pyramid's base area is \(60\cdot45=2700\,\text{cm}^2\); the removed smaller one's base area is \(40\cdot30=1200\,\text{cm}^2\). 4. Subtract their volumes: \(V=\frac{1}{3}\cdot2700\cdot150-\frac{1}{3}\cdot1200\cdot100=95000\,\text{cm}^3\). 5. Convert to liters: \(95000\,\text{cm}^3=95\,\text{L}\).

Answer

\(95\,\text{L}\)
Volume of pyramids, cones, and spheres 43
A square-pyramid frustum has a volume of \(700\,\text{cm}^3\). The lower base edge is \(10\,\text{cm}\), and the upper base edge is \(5\,\text{cm}\). Find the frustum height \(h\).

Hints

- Compare the upper and lower base edge lengths to find the similarity scale factor. - Model the frustum as a large pyramid with a smaller similar pyramid removed. - Express both pyramid heights in terms of one variable, then use the volume difference.

Solution

1. The upper base edge is half the lower base edge, so the small removed pyramid has linear scale factor \(\frac{1}{2}\) relative to the full pyramid. 2. Let \(H\) be the full pyramid height. Then the removed pyramid height is \(\frac{H}{2}\), so the frustum height is also \(\frac{H}{2}\). 3. The lower and upper base areas are \(100\,\text{cm}^2\) and \(25\,\text{cm}^2\). 4. Subtract the smaller pyramid's volume from the larger pyramid's volume: \(700=\frac{1}{3}\cdot100H-\frac{1}{3}\cdot25\left(\frac{H}{2}\right)=\frac{175H}{6}\). 5. Solving gives \(H=24\,\text{cm}\), so the frustum height is \(h=\frac{H}{2}=12\,\text{cm}\).

Answer

The frustum height is \(12\,\text{cm}\).
Volume of pyramids, cones, and spheres 44
A designer is creating a decorative bowl shaped like a cone frustum. The bowl must hold exactly \(1.5\,\text{L}\). Its top diameter is \(22\,\text{cm}\), and its bottom diameter is \(14\,\text{cm}\). Find the required depth in centimeters and round to the nearest tenth.

Hints

- Convert the diameters to radii and liters to cubic centimeters. - Extend the sides to form two similar cones. - Use the radius ratio to express both cone heights in terms of the bowl depth. - Set the difference of the cone volumes equal to the required capacity.

Solution

1. The top and bottom radii are \(11\,\text{cm}\) and \(7\,\text{cm}\), and \(1.5\,\text{L}=1{,}500\,\text{cm}^3\). 2. Extend the slanted sides below the bowl to form two similar cones. If the bowl depth is \(h\), similarity gives the smaller cone height \(\frac{7h}{4}\) and the larger cone height \(\frac{11h}{4}\). 3. The volume difference is \(1{,}500=\frac{1}{3}\pi\cdot11^2\left(\frac{11h}{4}\right)-\frac{1}{3}\pi\cdot7^2\left(\frac{7h}{4}\right)=\frac{247\pi h}{3}\). 4. Solving gives \(h=\frac{4{,}500}{247\pi}\approx5.7992\,\text{cm}\), so the required depth is \(5.8\,\text{cm}\).

Answer

The bowl must be approximately \(5.8\,\text{cm}\) deep.
Volume of pyramids, cones, and spheres 45
A concrete column is shaped like a cone frustum with volume \(150\,\text{dm}^3\). The lower radius is \(3\,\text{dm}\), and the upper radius is \(2\,\text{dm}\). Find the height \(h\) and round to the nearest hundredth.

Hints

- Model the frustum as a large cone with a smaller similar cone removed. - Use the radius ratio to relate the cone heights to the frustum height. - Set the difference of the two cone volumes equal to the given volume.

Solution

1. Extend the sides to form a large cone and a smaller similar cone. Let the frustum height be \(h\). 2. Since the radii are in the ratio \(3\) to \(2\), the smaller cone height is \(2h\), and the larger cone height is \(3h\). 3. The frustum volume is \(150=\frac{1}{3}\pi\cdot3^2\cdot3h-\frac{1}{3}\pi\cdot2^2\cdot2h=\frac{19\pi h}{3}\). 4. Therefore, \(h=\frac{450}{19\pi}\approx7.5389\,\text{dm}\), which rounds to \(7.54\,\text{dm}\).

Answer

The column height is approximately \(7.54\,\text{dm}\).
Volume of pyramids, cones, and spheres 46
A regular square pyramid has all eight edges equal in length to \(s\): the four base edges and the four lateral edges from the base vertices to the apex. a) Find the pyramid's perpendicular height \(h\) in terms of \(s\). b) Derive a formula for the volume \(V\) in terms of \(s\). c) Find the volume when \(s=4.5\,\text{cm}\). Round to the nearest hundredth.

Hints

- Use a right triangle inside the pyramid that contains the perpendicular height. - Find the diagonal of the square base. - Apply the Pythagorean theorem to find the height. - Substitute that height into the pyramid volume formula.

Solution

1. The square base has diagonal \(s\sqrt{2}\), so the distance from its center to a vertex is \(\frac{s\sqrt{2}}{2}\). 2. The perpendicular height, the center-to-vertex segment, and a lateral edge form a right triangle. Thus, \(h^2+\left(\frac{s\sqrt{2}}{2}\right)^2=s^2\). 3. Therefore, \(h^2=s^2-\frac{1}{2}s^2=\frac{1}{2}s^2\), so \(h=\frac{s\sqrt{2}}{2}\). 4. Since the base area is \(s^2\), \(V=\frac{1}{3}s^2\cdot\frac{s\sqrt{2}}{2}=\frac{\sqrt{2}}{6}s^3\). 5. For \(s=4.5\,\text{cm}\), \(V=\frac{\sqrt{2}}{6}(4.5)^3\approx21.48\,\text{cm}^3\).

Answer

a) \(h=\frac{s\sqrt{2}}{2}\) b) \(V=\frac{\sqrt{2}}{6}s^3\) c) \(V\approx21.48\,\text{cm}^3\)
Volume of pyramids, cones, and spheres 47
A measuring cup is shaped like a cone frustum. Its bottom radius is \(6\,\text{cm}\), its top radius is \(9\,\text{cm}\), and it holds \(1.8\,\text{L}\). Find its vertical height to the nearest tenth of a centimeter.

Hints

- Convert the capacity to cubic centimeters before setting up a volume equation. - Imagine completing the original cone and removing the smaller cone below the cup. - The two radii tell you how the full and smaller cone heights compare.

Solution

1. Convert the capacity: \(1.8\,\text{L}=1800\,\text{cm}^3\). 2. Imagine extending the sloping sides downward to complete a large cone, with a smaller cone below the cup. The radii are in the ratio \(9:6=3:2\), so the large and small cone heights are \(3h\) and \(2h\). 3. Subtract their volumes: \(1800=\frac{1}{3}\pi\cdot9^2\cdot3h-\frac{1}{3}\pi\cdot6^2\cdot2h=57\pi h\). 4. Therefore, \(h=\frac{1800}{57\pi}\approx10.05189\,\text{cm}\), or \(10.1\,\text{cm}\) to the nearest tenth.

Answer

The measuring cup is about \(10.1\,\text{cm}\) tall.
Volume of pyramids, cones, and spheres 48
A cone-frustum workpiece has volume \(703.7\,\text{cm}^3\), height \(6\,\text{cm}\), and lower-base radius \(4\,\text{cm}\). Find the upper-base radius \(r\) to the nearest tenth.

Hints

- Substitute the known values into the cone-frustum volume formula. - Rearrange the equation into quadratic form in the unknown radius. - Solve the quadratic equation using an appropriate method. - Reject any solution that is not meaningful as a radius.

Solution

1. Substitute into the cone-frustum volume formula: \(703.7=\frac{1}{3}\pi\cdot6\left(4^2+4r+r^2\right)=2\pi(r^2+4r+16)\). 2. Divide by \(2\pi\): \(r^2+4r+16=\frac{703.7}{2\pi}\). 3. Write the quadratic equation as \(r^2+4r+16-\frac{703.7}{2\pi}=0\). 4. The quadratic formula gives \(r=\frac{-4\pm\sqrt{16-4\left(16-\frac{703.7}{2\pi}\right)}}{2}\). 5. The two solutions are approximately \(7.9999\) and \(-11.9999\). A radius must be positive, so \(r\approx8.0\,\text{cm}\).

Answer

The upper-base radius is \(8.0\,\text{cm}\).
Volume of pyramids, cones, and spheres 49
A cone-shaped container has its point sealed and is held with the point down. Its top diameter is \(12\,\text{cm}\) and its height is \(18\,\text{cm}\). Liquid fills it from the point upward. a) Write a function \(V(h)\) for the liquid volume at fill height \(h\), where \(0\le h\le18\) and \(h\) is measured in centimeters. b) Find the volume when \(h=9\,\text{cm}\). c) At what fill height is the funnel half full by volume? Round to the nearest tenth.

Hints

- Compare the filled cone with the entire container using similar triangles. - Express the changing liquid radius in terms of its height. - For half the volume, use half the full capacity, not half the funnel's height. - Check that the solution is between the point and the rim.

Solution

1. The full cone has radius \(6\,\text{cm}\) and height \(18\,\text{cm}\). 2. By similarity, \(\frac{r}{h}=\frac{6}{18}=\frac{1}{3}\), so \(r(h)=\frac{h}{3}\). 3. Thus \(V(h)=\frac{1}{3}\pi(\frac{h}{3})^2h=\frac{\pi}{27}h^3\,\text{cm}^3\) on \(0\le h\le18\). 4. At \(h=9\), \(V(9)=27\pi\,\text{cm}^3\approx84.8\,\text{cm}^3\). 5. Full capacity is \(V(18)=216\pi\,\text{cm}^3\). Half capacity is \(108\pi\,\text{cm}^3\). 6. Solving \(\frac{\pi}{27}h^3=108\pi\) gives \(h=\sqrt[3]{2916}\,\text{cm}\approx14.3\,\text{cm}\), within the physical range.

Answer

a) \(V(h)=\frac{\pi}{27}h^3\,\text{cm}^3\), for \(0\le h\le18\). b) \(V(9)=27\pi\,\text{cm}^3\approx84.8\,\text{cm}^3\). c) \(h\approx14.3\,\text{cm}\).
Volume of pyramids, cones, and spheres 50
A solid stone pedestal is shaped like a right square-pyramid frustum. The lower base edge is \(60\,\text{cm}\), the upper base edge is \(40\,\text{cm}\), and the volume is \(76\,\text{dm}^3\). Find the pedestal height.

Hints

- Convert the volume to cubic centimeters. - Use the ratio of the two square edge lengths to relate the full and removed pyramid heights. - Write the frustum volume as the difference of two pyramid volumes and solve for height.

Solution

1. Convert the volume: \(76\,\text{dm}^3=76{,}000\,\text{cm}^3\). 2. The upper-to-lower edge ratio is \(40\div60=\frac{2}{3}\). If the full pyramid height is \(H\), the removed pyramid height is \(\frac{2H}{3}\), so the frustum height is \(\frac{H}{3}\). 3. The lower and upper base areas are \(3600\,\text{cm}^2\) and \(1600\,\text{cm}^2\). 4. The volume difference is \(76{,}000=\frac{1}{3}\cdot3600H-\frac{1}{3}\cdot1600\left(\frac{2H}{3}\right)=\frac{7600H}{9}\). 5. Thus, \(H=90\,\text{cm}\), and the frustum height is \(\frac{H}{3}=30\,\text{cm}\).

Answer

The pedestal is \(30\,\text{cm}\) tall.

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