Instead of actually showing any handy numerical processes used to figure out problems, this book tries to tell you via overly-wordy and remarkably garbled explanations in the middle of "real world" situations gathered from statistics. The authors' idea of "Informal" apparently means burying explanations under useless jargon. If you want to pass a Calculus class and don't already have a talent for mathematics, this is not the book to use. Use something that's straight to the point and ditch the "Informal Approach".