digits are written along the circumference, and it is known that if we start from a certain position and read these digits in a clockwise direction, the resulting 1953-digit number is divisible by 27. Prove that regardless of the starting position, reading the digits in a clockwise direction will always result in a 1953-digit number that is divisible by 27.
(16th Moscow Mathematical Olympiad, 1953)
Solution
[Proof] Let the 1953-digit number starting from a certain position be
Then, by the given condition, .
We only need to prove that is divisible by 27, and then, each time we move one digit from the end to the beginning, we can get all numbers divisible by 27.
Consider
Since and are both divisible by 27, then
1953
Also, , so .
Thus, is divisible by 27.
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