# Chapter 2 - Set Theory - Chapter 2 Test: 15

$n(A \cup B') = 5$

#### Work Step by Step

$n(A\cup B)$ represents the cardinality (or number of elements) of the set $A \cup B'$. RECALL: (1) $B'$ represents the complement of set $B$. The complement of a set is the set that contains all the elements of the universal set $U$ that are not in the set.. (2) $\cup$ represents union of sets. The union of two sets is a set that contains the combined elements of the two sets. Thus. $B' = \left\{a, b, g\right\}$ Therefore, $A \cup B' \\ =\left\{a, b, c, d\right\} \cup \left\{a, b, c, g\right\} \\=\left\{a, b, c, d, g\right\}$ $A \cup B'$ has 5 elements. Thus, $n(A \cup B') = 5$

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