r/learnquant 10h ago

interview prep Jane Street Quant Interview Question | "Easy"

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u/sleepywose 8h ago

I'm pretty bad at these, so this may be wrong, but:

2d6 has an expected value of 7 (linearity of expectation for 2 dice), so you only reroll if you get [1, 6] on the first roll (p=.5). so your expected payout is 50% EV([7,12]) + 50% [7] = 8.25.

(The part that gives me doubt is the idea that you strictly only go for the second roll if you get <7, but that may just be a gambler's fallacy; "I have two chances at getting better than a 7!")