Precalculus (10th Edition)

Published by Pearson
ISBN 10: 0-32197-907-9
ISBN 13: 978-0-32197-907-0

Chapter 13 - Counting and Probability - 13.1 Counting - 13.1 Asses Your Understanding - Page 847: 14



Work Step by Step

According to the counting formula we know that $n(A\cup B)=n(A)+n(B)-n(A\cap B).$ Hence here because $n(B)=n(A):$ $60=n(A)+n(A)-40\\2n(A)=100\\n(A)=50.$
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