If X and Y are two sets such that has 18 elements, X has 8 elements and Y has 15 elements; how many elements does `X nnY`have?

Explanation

To find the number of elements in the intersection of sets \(X\) and \(Y\) (denoted as \(X \cap Y\)), we can use the formula for the union of two sets:

\[ n(X \cup Y) = n(X) + n(Y) - n(X \cap Y) \]

Where:
- \(n(X \cup Y)\) is the number of elements in the union of sets \(X\) and \(Y\).
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