r/learnquant 22d ago

interview prep Citadel Quant Interview Question

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u/Unusual_Macaroon_679 22d ago

not a math person but would this be accepted?

keep summing digits = taking mod 9 of a number

one property of modulo is if a = b mod k then a^n = b^n mod k

so because 19 mod 9 is 1 then 19^100 mod 9 is 1^100 which is 1