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You can divide 6 into equal parts of 1, 2, 3, or 6 (but not 4 or 5) because 6 is divisible by these numbers. The rules of divisibility have wide-ranging applications as an easy test for divisibility.

If the number \(\overline{7448x24y}\) is divisible by \(72\), and \(x \ne y,\) find \(x-y\).

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\[ {\huge \color{blue}N = \color{green} {123,4}\color{red}{F}\color{green}{6,789}}\]

If \(\color{red} {F}\) is replaced with a digit from the set (0, 1, 2, 3, 4, 5, 6, 7, 8, or 9) at random, what is the probability that \(\color{blue} {N}\) will be divisible by 3?

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A longevity chain is a sequence of consecutive positive integers, whose digit sums are never a multiple of 9. What is the longest possible length of a longevity chain?

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\[ \begin{array} { l l l l } & && & A & A & A \\ \times & & & & A & A & A \\ \hline &A & A & 8 & 0 & 0 & 1\\ \end{array} \]

What is the three digit number \(\overline{AAA}?\)

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