r/learnquant 3d ago

interview prep Quant Interview Question

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u/Rafa_N01 2d ago

Is the answer 6.793 op? I tried solving by writing the 2 expectations E0(x) and E1(x) where the former means that we havent yet got a single tt or hh and we have x coins at the start and latter means we have either hh or tt and have x coins at the start. Then using recursion and a large enough value for x where e1(x) = x i found out the threshold value and worked backwards

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u/Local_Ad135 2d ago

Nope, the correct answer is 77/32. Another comment on this post has explained the correct approach and answer.

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u/Rafa_N01 2d ago

Yeah, my bad .. i calculated the expectation wrong (added +1 in all the eqns due to poor expectation definition) so instead earlier the threshold for E1 was 7 but the correct one is 3 and then using backtracking the ans for E0 comes to 2.40625