Question 7

Mathematics Sets Easy

The number of triples of sets (A,B,C) with\(A, B, C \subseteq \{1, 2, \dots, n\}\) Such that \((A \cap B) \subseteq C \subseteq (A \cup B)\)

(A) \( 5^n \)
(B) \( 6^n \)
(C) \( 7^n \)
(D) \( 8^n \)
✓ Correct Answer: Option B Verified Solution

📘 Step-by-Step Solution & Detailed Explanation:

Decide independently for each element x of {1, …, n}, based on where it sits relative to A and B:

  • x in both A and B: then x is in A ∩ B, so x must be in C. 1 way.
  • x in neither: then x is not in A ∪ B, so x must not be in C. 1 way.
  • x in A only: C can include it or not. 2 ways.
  • x in B only: 2 ways.

Total per element = 1 + 1 + 2 + 2 = 6, so the number of triples is \(6^n\).

Answer: (B) \(6^n\)

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