Suppose that X,Y and Z are subsets of {1, 2, 3, . . . , 10} and |X| = |Y| = |Z| = 7. (i) Prove that |X ∩ Y| ≥ 4. (ii) Deduce that X ∩ Y ∩ Z is non-empty. [Hint: Consider (X ∩ Y) ∪ Z.]

Elements Of Modern Algebra
8th Edition
ISBN:9781285463230
Author:Gilbert, Linda, Jimmie
Publisher:Gilbert, Linda, Jimmie
Chapter2: The Integers
Section2.1: Postulates For The Integers (optional)
Problem 25E: 25. Prove that if and are integers and, then either or. (Hint: If, then either or, and similarly...
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Suppose that X,Y and Z are subsets of {1, 2, 3, . . . , 10} and |X| = |Y| = |Z| = 7.
(i) Prove that |X ∩ Y| ≥ 4.


(ii) Deduce that X ∩ Y ∩ Z is non-empty.

[Hint: Consider (X ∩ Y) ∪ Z.]

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