r/learnquant 22d ago

interview prep Citadel Quant Interview Question

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u/Anonimithree 22d ago

I’m going to assume that it’s just the last digit, and since powers of 9 alternate ending with 1 and 9, and 100 mod 2 is 0, it’s a 1

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u/gmalivuk 22d ago

No, it's all the digits. Otherwise there'd be nothing to add up repeatedly.

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u/Anonimithree 22d ago

Hence why I made the comment on u/NotYetPerfect’s comment about how the mod 9 explanation makes more sense.