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

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Correct Answer: 5

Explanation:

Given in the question ,
n(X ∪Y) = 18, n(X) = 8, n(Y) = 15.
Using the formula
n(X ∩ Y) = n(X) + n(Y) – n(X ∪ Y), we get n(X ∩ Y) = 8 + 15 – 18 = 5.

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