Answer
$6$
Work Step by Step
By definition, $a\ mod\ 7=4$ means that $a=7q+4$ for some integer $q$. Therefore, $5a=5(7q+4)$$=7(5q)+20$$=7(5q)+7(2)+6$$=7(5q+2)+6$. Since $0\leq6\lt7$, we conclude that $5a\ mod\ 7=6$.
Discrete Mathematics with Applications 4th Edition
by Epp, Susanna S.
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 4.4 - Page 189: 20
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