Question
Given two numbers such that one is obtained from the other by changing the order of its digits. Prove that their difference is divisible by `9`.
Difficulty level (1 very easy - 10 very hard): 3
Topics:
Number Theory
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Modular Arithmetic / Remainder Arithmetic
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Divisibility Rules
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Divisibility Rules by 3 and 9
Proof and Example
Arithmetic
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Division with Remainder
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