Answer
$2.5$
Work Step by Step
$a_{m}-a_{n}=\left( m-n\right) d\Rightarrow a_{20}-a_{7}=\left( 20-7\right) d\Rightarrow 69-23.5=13d\Rightarrow d=3.5\Rightarrow a_{7}=a_{1}+6d\Rightarrow 23.5=a_{1}+6\times 3.5\Rightarrow a_{1}=2.5$
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 - 11.2 Arithmetic Sequences and Series - 11.2 Exercises - Page 1025: 37
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