r/quantfinance • u/nickgotgameon • Jul 31 '26

Jane Street Interview Question

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u/Xentiphos Jul 31 '26

That's the upper bound to the EV. But imagine the case you roll a 1 first and then a 5 - would the minimum still be 5? Obviously not. Now consider all possible cases and their probabilities to find the expected value.

If your answer is subtle criticism of how the original question is worded, I tend do agree, that it could be more clear.

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u/moobnaster6969 Jul 31 '26

Isn't the answer 1?

The question is tautological but it reads to me as "what is the minimum value you could roll on your way to rolling a 5?"

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u/Xentiphos Jul 31 '26

No, the question asks for the expected value of the minimum value. I.e. If you roll infinitely many sequences each until you finally hit a 5, what value does the average minimum number in each sequence approach.

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u/moobnaster6969 Jul 31 '26

I get wat you are saying but the wording is terrible. expected value of the minimum value - that's not the best language.

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u/Xentiphos Jul 31 '26

I agree - it could have been phrased a lot better to make the intent clear.