Q: Carlo has a music recital next week. He practiced twice as long on Monday as on Tuesday. On Tuesday, he practiced 10 minutes less than on Wednesday. On Wednesday, he practiced 5 minutes more than on Thursday. On Thursday, he practiced for 50 minutes. If he needs to practice for a total of 5 hours that week, how long should Carlo practice on Friday?
A: On Wednesday, Carlo practiced for 50 + 5 = 55 minutes. On Tuesday, he practiced for 55 - 10 = 45 minutes. On Monday, he practiced for 45 x 2 = 90 minutes. So, Carlo practiced for a total of 90 + 45 + 55 + 50 = 240 minutes from Monday to Thursday. He needs to practice for a total of 60 x 5 = 300 minutes. Therefore, he should practice for 300 - 240 = 60 minutes on Friday. The answer is 60.

Q: Peter has 20 books. He has read 40% of them. His brother has read 10% of them. How many more of these books has Peter read than his brother?
A: Peter has read 8 of these books because 20 x .4 = 8. His brother has read 2 of these books because 20 x .1 = 2. Peter has read 6 more books than his brother because 8 - 2 = 6. The answer is 6.

Q: A class has 500 tables and 2/5 times as many books as the number of tables in the class are on top of each table. What's the total number of books in the class?
A:
If there are 2 / 5 times as many books as the number of tables in the class on top of each table, there are 2 / 5 * 500 = 200 books. Since the class has 500 tables with 200 books on top of each, there are 500 * 200 = 100000 books. The answer is 100000.