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Submitted by @PeroK
Consider all 7-digit numbers which are a permutation of the digits 1-7. How many of these are divisible by 7?
Can you prove the answer algebraically, rather than simply counting them?
Please make use of the spoiler tag
Consider all 7-digit numbers which are a permutation of the digits 1-7. How many of these are divisible by 7?
Can you prove the answer algebraically, rather than simply counting them?
Please make use of the spoiler tag