#### Answer

7

#### Work Step by Step

$S_{n}=\dfrac {a_{1}+a_{n}}{2}\times n\Rightarrow a_{1}=\dfrac {2S_{n}}{n}-a_{n}\Rightarrow a_{1}=\dfrac {2\times S_{20}}{20}-a_{20}=\dfrac {2\times 1090}{20}-102=7$

Published by
Pearson

ISBN 10:
013421742X

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

7

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