Thinking Mathematically (6th Edition)

Published by Pearson
ISBN 10: 0321867327
ISBN 13: 978-0-32186-732-2

Chapter 5 - Number Theory and the Real Number System - 5.5 Real Numbers and Their Properties; Clock Addition - Exercise Set 5.5: 45

Answer

$1-4=-3$ 1 and 4 are natural numbers, but -3 is not.

Work Step by Step

Natural numbers are the counting numbers: 1, 2, 3, ... The set of natural numbers is not closed with respect to subtraction, as can be seen in the example below: 1 and 4 are natural numbers. However, $1-4 = -3$, which is not a natural number.
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