Thinking Mathematically (6th Edition)

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

Chapter 11 - Counting Methods and Probability Theory - 11.2 Permutations - Exercise Set 11.2 - Page 702: 72

Answer

The number of 4-digit odd numbers less than 6000 that can be formed is\[48\].

Work Step by Step

The number of 4-digit odd numbers less than 6000 that can be formed can be calculated by multiplying the possibility of numbers at each place. If a number is selected for the first place, then there are 2 ways to select as the number must be less than 6. The number of 2nd and 3rd place can be computed in\[_{4}{{P}_{2}}\]ways. Similarly for the 4th place there are 2 possibilities. Compute the number of 4-digit odd numbers less than 6000 that can be formed using the equation as shown below: \[\begin{align} & \text{Number of 4-digit odd numbers less than 6000}=\text{First place}\times \text{second place} \\ & \times \text{third place}\times \text{fourth place} \\ & =2{{\times }_{4}}{{P}_{2}}\times 2 \\ & =2\times \frac{4!}{\left( 4-2 \right)!}\times 2 \\ & =4\times \frac{4\times 3\times 2!}{2!} \\ & =48 \end{align}\]
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