Answer
See below.
Work Step by Step
We need to find a z-value with an area of $1-0.20=0.80$ to the left of z. Use Table-A, we can find $z\approx0.84$
See figure.
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 3 - The Normal Distributions - Apply Your Knowledge - Page 93: 3.13b
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