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# If $A\:and\:B$ are two sets such that $(A-B)\cup B=A$, then what can you say about $A\:and\:B$?

$\begin{array}{1 1} A\subset B \\ B\subset A \\ A=\phi \\ B=\phi \end{array}$

We know that $(A-B)\cup B=A\cup B$
But given that $(A-B)\cup B=A$
$\Rightarrow\:A\cup B=A$
$\Rightarrow B\subset A$