BECE Mathematics 2021 Paper

Concept: The intersection of two sets, written as $A \cap B$, contains only the elements that are present in both sets.Explanation: The given sets are $A = \{1,3,5,7,9,11,13,15\}$ and $B = \{3,6,9,12,15\}$.To find $A \cap B$, check each element of set $A$ to see if it also belongs to set $B$.The numbers $3$, $9$, and $15$ appear in both sets, while all other elements of $A$ are not present in $B$.Therefore, $A \cap B = \{3,9,15\}$.The notation $n(A \cap B)$ means the number of elements in the intersection set.The set $\{3,9,15\}$ contains exactly three elements, so we count them as $3$.Thus, $n(A \cap B) = 3$.Answer: $3$ (Option A).