Answer
$155$
Work Step by Step
$a_{1}=5;r=\dfrac {40}{20}=\dfrac {20}{10}=\dfrac {10}{5}=2\Rightarrow S_{n}=\dfrac {a_{1}\left( 1-r^{n}\right) }{1-r}=\dfrac {5\times \left( 1-2^{5}\right) }{1-2}=155$
Precalculus (6th Edition)
by Lial, Margaret L.; Hornsby, John; Schneider, David I.; Daniels, Callie
Published by
Pearson
ISBN 10:
013421742X
ISBN 13:
978-0-13421-742-0
Chapter 11 - Further Topics in Algebra - 11.3 Geometric Sequences and Series - 11.3 Exercises - Page 1033: 5
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