Invitation to Computer Science 8th Edition

Published by Cengage Learning
ISBN 10: 1337561916
ISBN 13: 978-1-33756-191-4

Chapter 3 - Exercises - Page 139: 2a


$78$ gifts --- We are interested in the number of gifts given on Day 12 for which we have 12 verses where each $n^{t h}$ verse adds $n$ gifts to the total amount. We can use the formula that is already known: $1+2+3+\ldots+n=\frac{n \cdot(n+1)}{2}$ Replacing 12 for $n$ in the formula yields $\frac{12 \cdot(12+1)}{2}=78$ So the number of gifts given on Day $12$ is $78 .$

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