Q: Julia collects old watches. She owns 20 silver watches, and three times as many bronze watches. She decided to buy gold watches to add to her collection, a number that represents 10% of all the watches she owns. How many watches does Julia own after this purchase?
A: Julia owns 3 * 20 = 60 bronze watches. 60 + 20 = 80 total silver and bronze watches. 10% of all Julia's watches is 80 * 10 / 100 = 8 watches, and she decided to buy so many gold watches. So in total Julia is in possession of 20 + 60 + 8 = 88 watches. The answer is 88.

Q: Dave bought 8 books about animals, 6 books about outer space, and 3 books about trains to keep him busy over the holidays. Each book cost $6. How much did Dave spend on the books?
A: Dave buys 8 books + 6 books + 3 books = 17 books in total. He has to spend 17 books $6 / book = $102 if he wants to buy all the books. The answer is 102.

Q: There are 10 books on the table. Two-fifths of them are reading books and three-tenths of them are math books. There is one fewer science book than math books and the rest are history books. How many history books are there?
A:
Out of the 10 books, 10 x 2 / 5 = 4 are reading books. While 10 x 3 / 10 = 3 are math books. There are 3 - 1 = 2 science books. So, the total number of reading, math, and science books is 4 + 3 + 2 = 9. Thus, there is only 10 - 9 = 1 history book. The answer is 1.