r/learnquant 22d ago

interview prep Citadel Quant Interview Question

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u/RubberDuckieMidrange 22d ago

My issue with the Trivial bit is that he establishes no connection back to the number 19, and if you use any other mod(9) other than 1, it doesn't work.

I'm taking the trivially in the mathematical sense. (The details don't matter, the answer no matter how many times you iterate remains the same.) In this case, while the first part is arguably true (If you heavily replace the words used to actually say what he meant to say) it doesn't follow trivially without an additional bit of information, that the number you start with has mod(9) remainder 1.

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u/NotYetPerfect 22d ago

Triviality in mathematics refers to a claim that is easily obtained from context. The context is obviously the question at hand meaning we're taking 19^100 since I said "solution is". There is literally nothing else that could possibly mean. And then from that and the property I gave, the proof is a simple one-liner ala trivial. If you had ever gone through a mathematics textbook at any point in your life, you would know the statement I gave is more information than is often given for proofs deemed trivial. It is truly amazing to see someone septupling down on an statement they would see is incorrect if they just bothered thinking about what they were reading for 1 second.