Q: Mary has a mystery book library. She started with 72 mystery books at the beginning of the year. She joined a book club that sent her 1 book each month of the year. She went to a bookstore halfway through the year and bought 5 more books, then bought 2 books at yard sales later. Her daughter gave her another book for her birthday, and her mother gave her a series of 4 books when Mary visited her. She donated 12 books she didn't want to read again to a charity shop and sold 3 to a used book store. How many books did she have at the end of the year?
A: Mary got 1 * 12 = 12 books from the book club. She bought 5 + 2 = 7 books. She was given 1 + 4 = 5 books. She got rid of 12 + 3 = 15 books. Thus, at the end of the year she had 72 + 12 + 7 + 5 - 15 = 81 books. The answer is 81.

Q: The Science museum sells dinosaur models for $100 each. A certain school bought 2 models for the kindergarten library and also bought twice as many for the elementary library. Since the school bought more than 5 models, there was a 5% reduction in price for each model. How much did the school pay in all?
A: The school bought 2 x 2 = 4 dinosaur models for the elementary library. So the school bought a total of 2 + 4 = 6 models. The price of each model was reduced by $100 x 5 / 100 = $5. Thus, each model cost $100 - $5 = $95. Therefore, the school paid a total of $95 x 6 = $570. The answer is 570.

Q: Nicky is trading baseball cards with Jill. If Nicky trades two cards worth $8 each for 1 card worth $21, how many dollars of profit does he make?
A:
First find the total cost of the two $8 cards: $8 / card * 2 cards = $16. Then subtract the cost of the cards Nicky gave away from the cost of the card he received to find his profit: $21 - $16 = $5. The answer is 5.