Answer
$32491$
Work Step by Step
$n=(\frac{z_{\alpha/2}\sigma}{E})^2$ (we have to round up)
$1-\alpha=0.99$, thus according to the table, $z_{\alpha/2}=z_{0.005}=2.575$.
$n=(\frac{2.575\cdot7}{0.1})^2=32490.06\approx32491$
The Basic Practice of Statistics 7th Edition
by Moore, David S.; Notz, William I.; Fligner, Michael A.
Published by
W. H. Freeman
ISBN 10:
146414253X
ISBN 13:
978-1-46414-253-6
Chapter 18 - Inference in Practice - Chapter 18 Exercises - Page 436: 18.42
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