Answer
$240$
Work Step by Step
Let $F=850, S=690,$ and $T$ be the number of students saw it twice, we have:
$850+690-T=6000-4700$
thus $T=240$
An Introduction to Mathematical Statistics and Its Applications (6th Edition)
by Larsen, Richard J.; Marx, Morris L.
Published by
Pearson
ISBN 10:
0-13411-421-3
ISBN 13:
978-0-13411-421-7
Chapter 2 Probability - 2.2 Sample Spaces and the Algebra of Sets - Questions - Page 25: 31
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