Question: The price of a book was $400. If the book's price is decreased by 15% and then increased by 40%, what is the final price of the book?
Answer: When the price of the book is decreased by 15%, the total price decrease is 15 / 100 * $400 = $60. The new price of the book becomes $400 - $60 = $340. The price of the book is then increased by 40 / 100 * 340 = $136. The final price of the book is $340 + $136 = $476. The answer is 476.

Question: Gretchen's local ice cream shop offers 100 different flavors. She was able to try a 1/4 of the flavors 2 years ago and double that amount last year. How many more flavors will she need to try this year to have tried all 100 flavors?
Answer: The shop offers 100 flavors and she tried 1 / 4 of the flavors so she had 100 * .25 = 25 flavors 2 years ago. Last year she ate double the amount from the previous year so she had 25 * 2 = 50 flavors. 2 years ago she ate 25 flavors and last year she had 50 flavors so she has had 25 + 50 = 75 flavors. The shop offers 100 flavors and she has had 75 flavors so she still needs to try 100 - 75 = 25 flavors. The answer is 25.

Question: At a station, a train comes every 5 minutes leaving 200 passengers and taking 320 others. How many different passengers step on and off a train at the station within an hour?
Answer: At every passenger exchange there are 200 + 320 = 520 different people. One hour is 60 minutes, so during one hour, a train comes 60 minutes / hour / 5 minutes / train = 12 times. So during one hour, 12 trains * 520 passengers / train = 6240 different passengers step on and off the train. The answer is 6240.

Question: Ashley had a birthday party and invited 20 of her friends, telling them to each invite one more person to attend the party. If half the number of the invited guests each came with one more person, what's the total number of people at the party, including Ashley?
Answer:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
If she invited 20 friends, then the number of friends who came with one more person is 1 / 2 * 20 = 10. If the 10 friends came with 10 more people, the total number of guests becomes 20 + 10 = 30 guests. If you add Ashley, the total number of people in the party is 30 + 1 = 31 people. The answer is 31.