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Below are four statements about three non-empty sets $P$, $Q$, and $R$ in a universal set $U$ - Junior Cycle Mathematics - Question 13 - 2018

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Question 13

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Below are four statements about three non-empty sets $P$, $Q$, and $R$ in a universal set $U$. (a) Put a tick ($\checkmark$) in the correct box in each case to ... show full transcript

Worked Solution & Example Answer:Below are four statements about three non-empty sets $P$, $Q$, and $R$ in a universal set $U$ - Junior Cycle Mathematics - Question 13 - 2018

Step 1

1. $\#(P \cup Q) = \#(P) + \#(Q)$

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Answer

This statement is sometimes true. While it's true for disjoint sets (where PQ=P \cap Q = \emptyset), it is not always true when sets overlap. For overlapping sets, the correct relation should reflect the intersection: #(PQ)=#(P)+#(Q)#(PQ)\#(P \cup Q) = \#(P) + \#(Q) - \#(P \cap Q).

Step 2

2. $P \cap Q = P \cap Q$

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Answer

This statement is never true. This is essentially a tautology; it cannot be true as it equates itself without giving any new information or significance. Therefore, it doesn't give a true representation of the relationship between the sets.

Step 3

3. $(P \cap Q)' = P' \cup Q'$

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Answer

This statement is always true. This is a direct application of De Morgan's Laws in set theory, which states that the complement of the intersection of two sets is equal to the union of their complements.

Step 4

4. $P \cup (Q \cap R) = (P \cup Q) \cap (P \cup R)$

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Answer

This statement is always true. This also follows from the distributive property of set operations, demonstrating how unions distribute over intersections.

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