For every acre of grass, the farmer can harvest 560 / 5 = 112 bales of hay each month. This year, the farmer has 7 + 5 = 12 acres of grass. He can expect to harvest 12 x 112 = 1344 bales of hay per month. The total hay production this year is 1344 * 12 = 16128. From September to December, the farmer would have to feed his horses for a total of 30 + 31 + 30 + 31 = 122 days. Each day his horse eats a total of 3 * 9 = 27 bales of hay. For the 122 days, the horses will eat a total of 27 * 122 = 3294 bales. The total number of bales remaining will be 16128 - 3294 = 12834.
The answer: 12834
Reverse engineering the question: A hay farmer harvested 560 bales of hay from 5 acres of grass per month last year. This year, he planted an additional 7 acres of grass. If the farmer also owns 9 horses and each horse consumes 3 bales of hay a day, how many bales of hay would the farmer have left by the end of December if he starts feeding them this year's hay beginning the first day of September?

If there are 30 students in Ms. Leech's class, and the number of boys is 10, the number of girls in Ms. Leech class is 30 - 10 = 20. If each boy brought 5 cups for the science activity, the total number of cups brought by the boys is 5 * 10 = 50 cups. The number of cups that the girls brought is 90 - 50 = 40 of the total number. Since the number of girls in the class is 20, each girl brought 40 / 20 = 2 cups each.
The answer: 2
Reverse engineering the question: There are 30 students in Ms. Leech's class. Twice as many girls as boys are in the class. There are 10 boys in the class and each boy today brought 5 cups for science activity class as Ms. Leech had instructed. If the total number of cups brought by the students in the class is 90, how many cups did each girl bring?

The candy bars cost 4 * 2 = $8. Todd has 20 - 8 = $12 left.
The answer: 12
Reverse engineering the question: Todd has $20. He buys 4 candy bars that cost $2 each. How much money in dollars does Todd have left?

There are 80 / 100 * 2300 = 1840 books in English at the library. Out of these books, only 60 / 100 * 1840 = 1104 were published inside the country. So there are 1840 - 1104 = 736 books in English published outside of the country.
The answer: 736
Reverse engineering the question:
In the school's library, there are 2300 different books. 80% of all the books are in English, but only 60% of these books were published in the country. How many English-language books have been published outside the country?