The capacity of Karson's home library is 400 books. If he currently has 120 books, how many more books does he have to buy to make his library 90% full? Give the rationale and then the answer.
Let's think step by step. When 90% full, Karson's library holds 90 / 100 * 400 = 360 books. If he has 120 books in the library now, he needs to buy 360 - 120 = 240 books to make his library 90% full.. The answer is: 240.

For every 12 cans you recycle, you receive $0.50, and for every 5 kilograms of newspapers, you receive $1.50. If your family collected 144 cans and 20 kilograms of newspapers, how much money would you receive? Give the rationale and then the answer.
Let's think step by step. There are 144 / 12 = 12 sets of 12 cans that the family collected. So, the family would receive $0.50 x 12 = $6 for the cans. There are 20 / 5 = 4 sets of 5 kilograms of newspapers that the family collected. So, the family would receive $1.50 x 4 = $6 for the newspapers. Therefore, the family would receive a total of $6 + $6 = $12.. The answer is: 12.

It takes 15 mink skins to make a coat. Andy buys 30 minks and each mink has 6 babies, but half the total minks are set free by activists. How many coats can he make? Give the rationale and then the answer.
Let's think step by step. First find the total number of baby minks: 30 minks * 6 babies / mink = 180 minks. Add this to the number of adult minks: 180 minks + 30 minks = 210 minks. Then divide this number in half to find how many aren't set free: 210 minks / 2 = 105 minks. Then divide the remaining number of minks by the number of minks per coat to find the number of coats: 105 minks / 15 minks / coat = 7 coats.. The answer is: 7.