Math Problem Statement

A square pyramid has a base edge of 32 inches and an altitude of 1 foot. A square pyramid whose altitude is one-fourth of the original altitude is cut away at the apex of the original pyramid. The volume of the remaining frustum is 112 cubic feet. A set of 8 square pyramids is created by slicing the original pyramid with three planes parallel to the base. Each pyramid is a dilation of the one cut away at the apex. Using the set of pyramids created, determine the number of subsets that contain at least one square pyramid with a volume less than or equal to 1 cubic foot.

Solution

To solve this problem, let's work through the details step by step:

Step 1: Understand the structure of the original and cut pyramid

  • Original Pyramid:

    • The base edge of the square is 32 inches.
    • The altitude (height) is 1 foot = 12 inches.
  • Cut Pyramid:

    • Its altitude is one-fourth of the original, so its height is 14×12=3\frac{1}{4} \times 12 = 3 inches.

Step 2: Calculate the volume of the original and cut pyramids

The formula for the volume of a square pyramid is: V=13×Base Area×HeightV = \frac{1}{3} \times \text{Base Area} \times \text{Height} where the base area for a square pyramid with edge aa is a2a^2.

  • Original Pyramid Volume:

    • Base area = 322=102432^2 = 1024 square inches.
    • Height = 12 inches.
    • Volume of the original pyramid: Voriginal=13×1024×12=122883=4096 cubic inchesV_{\text{original}} = \frac{1}{3} \times 1024 \times 12 = \frac{12288}{3} = 4096 \text{ cubic inches}
  • Cut Pyramid Volume:

    • Since the cut pyramid is similar to the original with height 33 inches (1/4th of the original height), the scale factor between the original and cut pyramid is 1:4.
    • Volumes of similar pyramids scale as the cube of their corresponding linear dimensions, so: Vcut=143×Voriginal=164×4096=64 cubic inchesV_{\text{cut}} = \frac{1}{4^3} \times V_{\text{original}} = \frac{1}{64} \times 4096 = 64 \text{ cubic inches}

Step 3: Calculate the volume of the frustum

  • The volume of the remaining frustum is given as 112 cubic feet. To work in consistent units, convert this to cubic inches: 112 cubic feet=112×123=112×1728=193536 cubic inches112 \text{ cubic feet} = 112 \times 12^3 = 112 \times 1728 = 193536 \text{ cubic inches}
  • The volume of the frustum is the difference between the volume of the original pyramid and the cut pyramid: Vfrustum=409664=4032 cubic inchesV_{\text{frustum}} = 4096 - 64 = 4032 \text{ cubic inches}

However, this calculated volume does not match the given volume of 193536 cubic inches. Let’s assume this mismatch is due to scaling of the problem and continue with the analysis of the set of 8 pyramids.

Step 4: Dilation of Pyramids

The problem states that 8 smaller square pyramids are created by slicing the original pyramid into parts that are each dilations of the one cut away at the apex. Each of these pyramids shares a similar structure, and their volumes will vary based on their heights.

  • Let’s denote the smallest cut pyramid as P1P_1, with a volume of 6464 cubic inches.
  • Since the problem mentions that each subsequent pyramid is a dilation, the heights and thus the volumes of these pyramids increase systematically as P1,P2,,P8P_1, P_2, \ldots, P_8.

Step 5: Determine the number of subsets containing at least one pyramid with V1V \leq 1

Since each pyramid is larger than the previous one in volume, if P1P_1 has a volume of 64 cubic inches, all subsequent pyramids will have volumes greater than 64 cubic inches.

  • This means no pyramids in the set of 8 have a volume less than or equal to 1 cubic inch.

Therefore:

  • The number of subsets that include at least one square pyramid with a volume less than or equal to 1 cubic foot is 0.

Would you like a breakdown of the calculations or have any questions? Here are five questions related to this problem:

  1. How is the volume of a frustum derived from two pyramids?
  2. What are the properties of similar solids when it comes to volume scaling?
  3. How do you convert cubic feet to cubic inches?
  4. What is the relationship between linear dimensions and volume in similar pyramids?
  5. Why does slicing a pyramid into smaller pyramids result in dilations?

Tip: When working with volumes of similar shapes, always remember that volume scales with the cube of the linear scale factor.

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Math Problem Analysis

Mathematical Concepts

Geometry
Volume of Pyramids
Similar Solids
Dilation

Formulas

Volume of a square pyramid: V = (1/3) * Base Area * Height
Volume scaling for similar solids: V2 = (Scale Factor)^3 * V1

Theorems

Similarity Theorem for Pyramids
Volume scaling theorem for similar solids

Suitable Grade Level

Grades 10-12