KöMaL 2021 K711
Ann's favourite number is 2468. Ben's favourite number also has four digits, and exactly two of its digits coincide with two digits of Ann's favourite number. Furthermore, each of the matching digits is in the same decimal place in both numbers. Based on this information, how many four-digit positive integers are there which may be Ben's favourite number?
Official text KöMaL. Quoted with source.
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