![\"\"](\"/userfiles/image/steps_images/step1.JPG\")
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n( AUB ) = 60, n( A∩B ) = 40 and n(A) = n(B). \ \
\By using counting formula : n( AUB ) = n(A) + n(B) − n( A∩B ) \ \
\Substitute : n( AUB ) = 60 , n( A∩B ) = 40. \ \
\60 = n(A) + n(B) − 40 \ \
\Substitute n(A) = n(B) \ \
\60 = n(A) + n(A) − 40 \ \
\60 = 2n(A) − 40 \ \
\2n(A) = 40 + 60 \ \
\![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=f6255f7712b2a29d9fb8826dde015e46.png\")
(Divide each side by 2)
n(A) = 50
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![\"\"](\"/userfiles/image/steps_images/solution.JPG\")
n(A) = 50