Confidence Interval Questions from Jane Street

I was just wondering what kind of questions these are. I heard they ask you to give confidence intervals for your answers, but I don't understand how you can do that (i.e. how would we find the margin of error when all you've done is found an answer to a brainteaser?). Also, I was curious as to how hard these questions can be, since I always thought confidence interval was just memorizing the standard error and then multiplying it by z alpha.

I have a first round interview with them for the trading internship position.