Q: Grace can read a 200-page book in 20 hours. How long would it take her to finish reading a 250-page book at this constant rate?
A: Grace can read 200 / 20 = 10 pages in 1 hour. So she can finish a 250 - page book in 250 / 10 = 25 hours. The answer is 25.

Q: Michonne is inviting her friends to her birthday party. She invites 6 of her friends from school and 12 of her friends from her neighborhood. Each of her friends asks if they can bring two friends along as well. How many people are going to Michonne’s birthday party?
A: Michonne has invited 6 + 12 = 18 friends. These friends have invited another 18 friends * 2 = 36 people. So in total, there are 18 friends + 36 people = 54 people going to Michonne’s party. The answer is 54.

Q: Charles is jogging while listening to his favorite album. He runs at 6 MPH when he's got music on and 4 MPH when he doesn't. His album is 40 minutes long. How many minutes will it take him to jog 6 miles?
A:
He runs at .1 miles per minute because 6 / 60 = .1. While the album is playing he can run 4 miles because 40 x .1 = 4. He has to run 2 miles without the album because 6 - 4 = 2. Without music he runs 1 / 15 miles per minute because 4 / 60 = 1 / 15. He will run the remaining 2 miles in 30 minutes because 2 / (1 / 15) = 30. It will take him 70 minutes in total because 40 + 30 = 70. The answer is 70.