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# If $A=\{1,2,3,4\},B=\{3,4,5,6\},C=\{5,6,7,8\}$ and $D=\{7,8,9,10\}$ Find (i) $A\cup B$

$\begin{array}{1 1}(A)\;\{1,2,3,4\}\\(B)\;\{1,2,3,4,5,6\}\\(C)\;\{1,2,3,4,5\}\\(D)\;\text{None of these}\end{array}$

$A\cup B=\{1,2,3,4\}\cup \{3,4,5,6\}$
$\Rightarrow \{1,2,3,4,5,6\}$
Common element of the given sets have been taken only once while writing $A\cup B$
Hence (B) is the correct answer.