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8*7*6*5*4 = 6720 different 5-digit numbers. ANSWER
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It is of the same type problem as another one (a TWIN) solved under this link
https://www.algebra.com/algebra/homework/Permutations/Permutations.faq.question.1173428.html
https://www.algebra.com/algebra/homework/Permutations/Permutations.faq.question.1173428.html
The same mantra works.