The scoring algorithm is not a simple thing to describe. If you finish all of the questions, and are able to give each a reasonable attempt, you will find (if you ever get the chance to see how your score evolved during the test) that your score changed most drastically during the first few questions. This is why some books say the first few questions are more important. If, however, you need to guess on the last several questions, you will find that your score can change just as drastically at the end of the test as at the beginning. Books that claim that the 'first ten' questions predominantly determine your score are grossly oversimplifying the scoring algorithm- if you spend so much time early in the test to get the first questions right that you don't have time to finish without guessing, your score will fall dramatically at the end of the test. It is true, to a very small extent, that early questions are more important than later ones, but you should only take this to mean that you won't suffer much by guessing at one (or maybe two) questions at the end- any more than that, and you risk seeing your score fall precipitously.