Answer
$B$
Work Step by Step
The sum is the sum of the first 20 natural numbers.
Using the trick of Gauss,
$20+1=21$
$19+2=21$
$18+3=21$
$...$
$11+10=21$
(all 20 numbers are used up)
Ten pairs, each adding to 21, total to $10\times 21=210$
Algebra 2 (1st Edition)
by Larson, Ron; Boswell, Laurie; Kanold, Timothy D.; Stiff, Lee
Published by
McDougal Littell
ISBN 10:
0618595414
ISBN 13:
978-0-61859-541-9
Chapter 12 Sequences and Series - 12.1 Define and Use Sequences and Series - 12.1 Exercises - Skill Practice - Page 799: 58
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