The essential point of the book is to show students in Introductory Chemistry classes how to obtain answers that are at least reasonable, and to realize when there must have been an error because the answer falls outside the range of possible values. Students often leave ridiculous answers because they simply plug into equations they have memorized (correctly or incorrectly). They have not learned to think about the meaning of the numbers that appear in their calculations. This book attempts to show students how to correct this.