document.write( "Question 1195725: Given that A and B are sets such that n(A) = 8, n(B) = 12 and n(AnB) = 3, find n(AnB) \n" ); document.write( "

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document.write( "n(AnB) is 3, which is already given.  
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document.write( "You probably meant to ask 'find n(AuB)' (?), in which case n(AuB) = 8+12-3 = 17.
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document.write( "The number of elements in the intersection is subtracted once because it is counted twice (once in A and once in B).  See inclusion-exclusion principle.   \n" );
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