KöMaL 2008 K168
Consider all possible seven-digit numbers formed by using each of the digits 1, 2, 3, 4, 5, 6, 7 once. ) Show that the difference of any pair of such seven-digit numbers is divisible by 9. ) How many pairs of different numbers can be selected out of them, such that one is a factor of the other?
Official text KöMaL. Quoted with source.
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