So by saying "C does not know", you give away that it can't be June or December, because these are the only months for which C could possibly know the birthday. Month knower knows both of them at this point cannot choose between Sep 1 and 5 and hence first said: "I don't know A's birthday, C doesn't know either. If it was information about any month other than June, I don't see how he could work it out (given still multiple options in the other months).

Pick this up if you're looking for help with different technical questions or more insight into what the interview, and subsequent job, will be like. With the initial interview largely assessing analytical skills, subsequent interviews may focus on in-depth quant concepts related to the industry and to broader personality characteristics, such as how you weigh a given set of options, how you manage your time and why you’re drawn to working in that particular industry.The book covers the interview process, options pricing, probability, rates, numerical methods, general mathematics, C++ and brainteasers. The book covers a variety of topics that you are likely to encounter in quantitative brain teasers, calculus, linear algebra, probability, stochastic processes and stochastic calculus, finance and programming. In fact, just by working through all the probability and statistics courses you will be well on your way to being able to answser most of the questions in the interview books.

We can exclude Dec and June months only because the month-knowing person tells us C does not have a chance. Because such organizations often operate at a fast pace and the decisions staff make can have far-reaching economic and financial impacts, interviewers seek to assess an applicant’s mathematical mastery, critical thinking skill and creativity, as well as the ability to perform under pressure.The first four chapters discuss a quant career as well as how to begin hunting for one, finally concluding with tips for interview. For in-person interviews, you may be handed a pencil and paper or markers for a whiteboard for your calculations. In this book we analyze solutions to more than 200 real interview problems and provide valuable insights into how to ace quantitative interviews.