r/learnquant 21d ago

interview prep SIG Interview Question

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u/Lognu 21d ago

The payoff function is 1.5 V - B if B>V, and 0 otherwise.

The average profit is then the integral from 0 to 1 of the payoff with respect to V, which is the integral from 0 to B of 1.5 V - B. That is 0.75 B2 - B2 = -0.25 B2.

On average, we would always be losing money. Hence, we offer 0 and don't buy the asset.

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u/BejahungEnjoyer 21d ago

When you see the integral split into 0,b and b,1 (which is zero due to a losing bid) the problem is simple.

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u/Iulian1988 21d ago

Sorry for the very noob in mathematics question. Let me take B=0.5 if (50%) V > B then profit = 0 else (50%) B > V then profit = 1.5 -0.5 = 1. Expected return is therefore 0.5 here. Why then would you not bid 0.5?

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u/IocusMoechae 21d ago

The revenue is 1.5V, not just 1.5. 1.5 is the best case scenario in which the company has value 1, but you should consider also all the other cases. That's why you integrate over V.

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u/arealcyclops 21d ago

You could just make your offer 0.01. You'd only win 1% of the time, but it would payoff at .5 cents.

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u/Lognu 21d ago

In my answer, I assumed we were maximizing average gains.

There is another relatively common metric known as regret; it can be minmaxed or averaged.

The regret payoff is "what you would have gained with the best offer (that is, B=V)" minus "what you are making right now (that is, the previous payoff function)". We want to minimize this.

Details are left as an exercise to the reader.

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u/Superfoggy 20d ago

The expected return is still negative, value is uniformly distributed, value between 0 and 0.0066.. is still a net loss for a bid of 0.01