Is it just me, or is that book full of typo's and various errors? I think the book in itself is a terrific idea, but if it was proofread. In some explanations, they use the wrong number, or use the wrong information. I thought it might have been just my misunderstanding, until I saw some of their numbers came from irrelevant previous parts of the problem, or even previous problems all together. Has anyone besides me noticed it?