#### Answer

$2.5$

#### Work Step by Step

$a_{m}-a_{n}=\left( m-n\right) d\Rightarrow a_{20}-a_{7}=\left( 20-7\right) d\Rightarrow 69-23.5=13d\Rightarrow d=3.5\Rightarrow a_{7}=a_{1}+6d\Rightarrow 23.5=a_{1}+6\times 3.5\Rightarrow a_{1}=2.5$

Published by
Pearson

ISBN 10:
013421742X

ISBN 13:
978-0-13421-742-0

$2.5$

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