Question 1193916
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How the problem is worded in the textbook, it is defective formulation, because it  NOWHERE says that repetition of digits is not allowed.


Very strange textbook. Probably, it is some home-made feature, which was never peer-reviewed.


Can you post the name of this textbook and its ISBN ?



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Edwin, I see from your post that you try to explain me something. Thanks for your attempt.


But what was written in my post, was not a question "if repeating is allowed or not ?"


It was a statement, saying that the problem formulation is defective, because it does not indicate directly,

if repeating is allowed or not.



When similar problem is formulated, such indication must be presented directly in the problem; 
a reader should not extract this info from the answer or to guess it based on the context.