# of ways to pick 2 books out of several sets of books. 1. The problem statement, all variables and given/known data A student has to sell 2 books from a collection of 6 math, 7 science, and 4 economics books. How many choices are possible if the books are to be on different subjects? 3. The attempt at a solution I'm sure if im right or the book. Analyzing one book, there are 6 ways to choose among the math, 7 ways the science, and 4 ways the economics. That makes 6x7x4 ways of choosing books. So for two books to be different, it would have to be half that amount. So (6x7x4)/2=84 ways. But the book has 94ways. So am I wrong? Even so, 84 is only 10 away from 94 so something about my reasoning is somewhat correct.