Answer
50
Work Step by Step
By using the counting formula for finite sets:
$n(A\cup B)= n(A) + n(B) - n(A\cap B)$
By substituting:
$60 = n(A) + n(B) - 40$
$60 = 2n(A) - 40$
$n(A)=50$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.