Elementary Statistics: A Step-by-Step Approach with Formula Card 9th Edition

Published by McGraw-Hill Education
ISBN 10: 0078136334
ISBN 13: 978-0-07813-633-7

Chapter 4 - Probability and Counting Rules - 4-4 Counting Rules - Exercises 4-4 - Page 237: 49


28 Dominoes

Work Step by Step

Each domino has two parts and each part can have 0 to 6 pips. The total possible combinations excluding doubles is $7\times6$=42 However, due to the symmetry, 12 is the same as 21 etc. so we only need half of 42 which is 21. We also need to add the 7 doubles (00,11,22,33,44,55,66) to 21, so there are 28 dominoes in a complete set with no repetitions.
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