Divisibility Rule for 9 | Math Olympiad | Number Theory | Mathematical Proof

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We are going over the divisibility rule for 9 so you will have a quick and easy way to tell whether a number is divisible by 9.
In this video, we will go through some important mathematical concepts. First, we will touch on the meaning of “if and only if”, which comes up a lot in mathematical statements including those in olympiad questions. Secondly, we show you how to construct a mathematical proof that is of acceptable quality as answer in olympiads. Finally, you actually learn the divisibility rule for 9 so you can apply it in the future when asked upon!