Math Problem Statement

Let A_1, A_2, A_3 be subsets of the set {1, 2, 3, 4, 5} such that (A_1 ∪ A_2) ∩ (A_2 ∪ A_3) = {1, 2, 3, 4, 5}. Let N be the number of ways to construct the list of sets (A_1, A_2, A_3). Find the last two digits of N.

Solution

The problem states that we have subsets A1,A2,A3A_1, A_2, A_3 of the set {1,2,3,4,5}\{1, 2, 3, 4, 5\}, and they need to satisfy the condition:

(A1A2)(A2A3)={1,2,3,4,5}.(A_1 \cup A_2) \cap (A_2 \cup A_3) = \{1, 2, 3, 4, 5\}.

This means that every element in the set {1,2,3,4,5}\{1, 2, 3, 4, 5\} must belong to both A1A2A_1 \cup A_2 and A2A3A_2 \cup A_3.

To satisfy this condition, each element in {1,2,3,4,5}\{1, 2, 3, 4, 5\} must appear in either:

  • A1A_1 or A2A_2, and
  • A2A_2 or A3A_3.

Analysis for Each Element

For any element x{1,2,3,4,5}x \in \{1, 2, 3, 4, 5\}:

  1. It can belong to both A1A_1 and A3A_3 independently.
  2. It must be in at least one of A1A_1 or A2A_2 and at least one of A2A_2 or A3A_3.

This results in the following possible placements for each element xx:

  1. xA1x \in A_1 and xA3x \in A_3.
  2. xA1x \in A_1 and xA3x \notin A_3.
  3. xA1x \notin A_1 and xA3x \in A_3.
  4. xA2x \in A_2 only (if xx is not in either A1A_1 or A3A_3).

Each element has 4 possible configurations to satisfy the condition.

Total Configurations

Since there are 5 elements in {1,2,3,4,5}\{1, 2, 3, 4, 5\}, and each element can be assigned to A1A_1, A2A_2, and A3A_3 in 4 ways to satisfy the condition, the total number of ways to assign elements is:

N=45=1024.N = 4^5 = 1024.

Finding the Last Two Digits of NN

To find the last two digits of 10241024, we calculate 1024mod1001024 \mod 100:

1024mod100=24.1024 \mod 100 = 24.

Answer

The last two digits of NN are 24\boxed{24}.

Would you like more details on any part of the solution, or do you have further questions?


Here are some related questions that expand on this concept:

  1. What if the set had more elements, say {1,2,,6}\{1, 2, \dots, 6\}? How would the answer change?
  2. How would the solution be affected if we required every element to appear in A1A_1 or A3A_3 but not necessarily in A2A_2?
  3. What if we changed the condition to (A1A2)(A2A3)={1,2,3,4,5}(A_1 \cap A_2) \cup (A_2 \cap A_3) = \{1, 2, 3, 4, 5\}?
  4. Can you generalize this approach to subsets A1,A2,,AnA_1, A_2, \ldots, A_n?
  5. How would the answer differ if we were only asked for the number of ways to create each subset without regard to the specific ordering of A1,A2,A_1, A_2, and A3A_3?

Tip: When analyzing sets with union and intersection conditions, consider each element independently and account for the constraints it must satisfy across the sets.

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Math Problem Analysis

Mathematical Concepts

Set Theory
Union and Intersection of Sets
Combinatorics

Formulas

Union and Intersection of Sets
Counting configurations

Theorems

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Suitable Grade Level

Grades 11-12