Q: John can read a book 60% faster than his brother. If his brother takes 8 hours to read a book, how long would it take John to read 3 books?
A: Reading 60% faster means John's brother takes 1 + .6 = 1.6 times as long as John to read. So John reads a book in 8 / 1.6 = 5 hours. So it would take John 5 * 3 = 15 hours to read 3 books. The answer is 15.

Q: Janessa has a plan to give her brother Dexter his first collection of baseball cards. She currently has 4 cards in addition to the 13 that her father gave her. She ordered a collection of 36 cards from eBay. After inspecting the cards she found 4 cards are in bad shape and decides to throw them away. Janessa ended up giving Dexter 29 cards. How many cards did Janessa keep for herself?
A: Janessa starts with 4 cards + 13 cards = 17 cards. She adds 17 cards + 36 cards = 53 cards from the eBay purchase. Janessa decides to throw away 53 cards - 4 cards = 49 cards due to damage. After giving Dexter the present we know that Janessa kept 49 cards - 29 cards = 20 cards for herself. The answer is 20.

Q: A certain tree was 100 meters tall at the end of 2017. It will grow 10% more than its previous height each year. How long has the tree grown from 2017 until the end of 2019?
A:
At the end of 2018, the tree will grow 100 x 10 / 100 = 10 meters more. Thus, its height at the end of 2018 is 100 + 10 = 110 meters. At the end of 2019, the tree will grow 110 x 10 / 100 = 11 meters more. So, its height at the end of 2019 is 110 + 11 = 121 meters. Therefore, the tree has grown 121 - 100 = 21 meters. The answer is 21.