Answer
$78$ gifts
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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 $78 .$
Work Step by Step
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