I`m just going over this book a second time and, as someone who has a mathematics degree, it`s really not that bad for mistakes. Admittedly the trigonometry chapter is pretty hideous once you reach the questions on page 67 - Qn 14 part c on page 68: the date in part c). should be 1st May 1990 - not 1st April! Also if these types of questions are not asked in radians you have to convert the answwer you get INTO radians.
That said, there aren`t that many mistakes, and you shouldn`t get too hung-up if some of your answers doesn`t agree with the book. It is reasonably well written, well laid out, and there are lots of different "demonstration" questions, graded in difficulty to increase your confidence as you go along. The only thing the book seems to be missing is simultaneous equations. The section on inverse functions could be more detailed, and explain that, to get the inverse of a function that is invertible (one-to-one) you set, in the original equation, x = f(y) and solve for the inverse y = ...
Overall a decent book. On a scale of 1 - 10 i`d give it an 8!