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 - 5.1 Number Theory: Prime and Composite Numbers - Exercise Set 5.1 - Page 256: 70



Work Step by Step

A number is divisible by 9 if the sum of its digits is a multiple of 9. Add the digits of the number to obtain: $=2+3+4+2+d \\=11+d$ Since $0 \le d \le 9$, the only possible value of $11+d$ that is a multiple of 9 is 18. Thus, $d$ must be 7.
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