Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

Published by Pearson
ISBN 10: 0-32184-874-8
ISBN 13: 978-0-32184-874-1

Chapter 14 - Sequences, Series, and the Binomial Theorem - 14.2 Arithmetic Sequences and Series - 14.2 Exercise Set: 41

Answer

$S_{20}=1030$

Work Step by Step

The first n term of an arithmetic sequence can be calculated as: $S_n=\frac{n}{2}(a_1+a_n)$ We have to find the 20th term first: $a_{n}=a_1+d\times(n-1)$ $a_{20}=4+5\times(20-1)=4+95=99$ Therefore we can substitute in the formula of the sum, and we get: $S_{20}=\frac{20}{2}(4+99))=10\times103=1030$
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