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Reduced to single digit (Posted on 2019-09-06) Difficulty: 3 of 5
Suppose that we have two operations that we can perform on an integer:

Multiply it by any positive integer.
Delete the 0's in its decimal representation.

Beginning with any positive integer can we always obtain a single-digit number after a finite number of operations? For example, beginning with 7, we can multiply by 15 to obtain 105, delete the 0 to get 15, multiply by 2 to get 30, then delete the 0 to end with 3.

No Solution Yet Submitted by Danish Ahmed Khan    
Rating: 3.0000 (1 votes)

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re(4): Possible solution | Comment 11 of 14 |
(In reply to re(3): Possible solution by Steven Lord)

Indeed the original was that 111 could not be reduced. Since 111 can be multiplied by 9 to get 999 at the next step, showing that 999 can be reduced also shows that 111 can also.
  Posted by Charlie on 2019-09-13 20:46:43

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