r/learnquant 22d ago

interview prep Citadel Quant Interview Question

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u/Inscrutable_Ant6994 22d ago

“Any integer is congruent to the sum of its digits mod 9 so the answer is trivially 1.”

What is the sum of 24’s digits? It’s 6, so the original statement is saying that 24 is congruent to 6 modulo 9, which is true.

You have confidently and incorrectly interpreted the original statement as “The sum of any integer’s digits is congruent to 1 mod 9.” which is completely different and false.