Discrete Mathematics with Applications 4th Edition

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

Chapter 9 - Counting and Probability - Exercise Set 9.3 - Page 553: 37

Answer

$400$ numbers.

Work Step by Step

For any number from 1 to 1000, there is a $1/2$ chance of it being divisible by 2 and a $1/5$ chance of it being divisible by 5. As al residues are evenly distributed from 1 to 1000, we can find the proportion of relatively prime numbers by doing $(1-1/2)(1-1/5) =2/5$, so the answer is $1000 * 2/5 = 400$
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