Please see the attached file for the complete solution.
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The first thing that you need to do with this problem is the subtraction inside the parenthesis ( ), which changes the problem into
What the exclamation point means is to multiply 89 by every whole number less than it, stopping at 1, so . Unfortunately, that is a lot of writing. However, we can write the multiplication and stop at any ...
A permutation is solved using factorials. The solution is detailed and well presented.