Question. At a certain bookstore, the best-selling book, "TOP," costs $8. The least-selling book, "ABC," costs $23. Thirteen "TOP" books and four "ABC" books were sold last week. What is the difference in the bookstore's earnings on these two books last week?
Answer. 12
What step-by-step reasoning justifies that answer?
Reasoning: On "TOP" books the bookstore made 13 * 8 = $104. The "ABC" books, on the other hand, were sold for a total of 4 * 23 = $92. The difference between earnings from these two books is 104 - 92 = $12.