College Algebra 7th Edition

Published by Brooks Cole
ISBN 10: 1305115546
ISBN 13: 978-1-30511-554-5

Chapter 8, Sequences and Series - Section 8.2 - Arithmetic Sequences - 8.2 Exercises: 74

Answer

$840$ cars

Work Step by Step

We know the sequence is: $20, 22, 24$ ... We need to sum $21$ terms. Since this is an arithmetic sequence with $d=2$, we plug in: $S_n=\frac{n}{2}[2a_1+(n-1)d]$ $S_{21}= \frac{21}{2}[2(20)+(21-1)(2)]=10.5*(40+40)=840$
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