Discrete Mathematics with Applications 4th Edition

Published by Cengage Learning
ISBN 10: 0-49539-132-8
ISBN 13: 978-0-49539-132-6

Chapter 4 - Elementary Number Theory and Methods of Proof - Exercise Set 4.3 - Page 179: 45

Answer

Since $n = 10a+5 = 5(2a+1)$, this is true.

Work Step by Step

Since $n$ ends in $5$, it can be written as $10a+5$ for some $a$. Therefore, it can be factored as $5(2a+1)$, so it is divisible by $5$, so this statement is proven true.
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