If you ask someone to choose ten random digits (not including 0) and multiply them all together, then to tell you all but one of the digits of the answer, you can predict the remaining digit.

Good luck proving it!

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## Comments

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TopNewestWhat do you mean? If I choose ten '1's, their product is 1. So I will tell that person nothing (all but one). However there are many possible digits.

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If there were a dislike button I would have pressed it.

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Let the random digits be \(a_1, a_2, a_3, \ldots, a_{10}\) \(\Huge\mbox{NOT}\) respectively, where \(a_{10}\) is the digit not told to you.

The product will be \(P=a_1a_2a_3\ldots a_{10}\), and the digits told to you will be \(a_1, a_2, a_3, \ldots, a_9\).

The remaining digit is obtained by dividing \(P\) by \(a_1, a_2, a_3, \ldots, a_9\) one by one, which equals to \(a_{10}\).

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This is an extremely fun question, as well as easy. :)

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