Ten > Sets
If n(X) = 40, n(Y) = 60 and n(X $\rm \cup$ Y) = 85, then find n(X $\rm \cap$ Y) and no(Y) by using formula.
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Solution
Given
$\rm n(X) = 40, n(Y) = 60, n(X \cup Y) = 85$
By using the formula for the union of two sets, we get
$\rm n(X \cup Y) = n(X) + n(Y) - n(X \cap Y)$
$\rm or, n(X \cap Y) = n(X) + n(Y) - n(X \cup Y)$
$\rm or, n(X \cap Y) = 40 + 60 - 85$
$\rm \therefore n(X \cap Y) = 15$
Now, we show the above information in a Venn diagram.

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