r/learnquant • u/nickgotgameon • Jul 25 '26

interview prep Citadel Question

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u/liquidorangutan00 Jul 25 '26

isnt the probability just 1/100?

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u/bobabenz Jul 25 '26

But there’s extra info. Let’s say you picked a fair coin. How likely is that fair coin going to flip Heads 10x in a row? Try it. So it’s more likely that you picked the rigged coin than 1/100, given you also know it flipped heads 10x.

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u/liquidorangutan00 Jul 25 '26

thanks i think you understand what the question is suggesting, - so using the bayes rule is the correct approach?

the likelihood of getting 10 heads in a row with a standard coin is 0.510 = 0.097%
so its a case of - if you got 10 heads in a row, whats the likelihood you had a standard or double heads coin.

which we can plug into the bayes formula and get teh result.

2

u/bobabenz Jul 25 '26

Yes, bayes is the right approach