We interview people at work, from time to time. We like setting interviewees puzzles. Moreover, we like puzzles anyway, and interview puzzles are generally good ones. So, this book is full of interview puzzles (generally for finance jobs), ranging from purely general puzzles through to ones based around options, finance and probability.
One of the things I found most interesting, in fact, was how many of the puzzles I'd seen before, some even while still in school. Others I'd first heard in my job, and it really does seem that there's a common pool of interview questions. Presumably there's a bit of an arms race between puzzle manufacturers and the guy who publishes this book (which proudly proclaims 'revised 9th edition' on the front). Another interesting thing is how the questions vary so widely in difficulty, although this might be explained in terms of 'warm-up' and 'challenging' questions.
All-in-all, the book's quite a nice set of brain-teasers with a financial edge on it, although presumably it sells rather better as a short-cut to getting a good job without thinking too hard.