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**alvinero****Member**- Registered: 2017-07-31
- Posts: 1

Hello, a friend of mine suggested me this problem:

Find a number n that, when you swap the first and last digits, it becomes 2n. Please, try to find it in decimal system.

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Hi alvinero,

Welcome to the forum. Any restrictions on the number of digits? For instance, n = 0 works. Two digits can be ruled out by letting n = 10a + b (which has no solutions as per your constraints), and three digits can also be ruled out the same way via modulo arithmetic. If a non-trivial solution exists, it may be large.

EDIT: I have a solution, but it is 21 digits long. I don't know if this is the smallest such solution (and, if this was intended to be a quick brain teaser, it seems unlikely to be). I'll post up a rough solution tomorrow.

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Apparently the smallest number has 18 digits.

https://www.youtube.com/watch?v=1lHDCAIsyb8

https://mindyourdecisions.com/blog/2017 … ay-puzzle/

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Thanks for the solution, it is an interesting problem.

**LearnMathsFree: Videos on various topics.New: Integration Problem | Adding FractionsPopular: Continued Fractions | Metric Spaces | Duality**

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