The carpenter initially has 8 x 5 = 40 blocks of wood. So he still lacks 80 - 40 = 40 blocks of wood. Therefore he still needs 40 / 5 = 8 logs of wood.
The answer: 8
Reverse engineering the question: A carpenter is building a house. He needs 80 woodblocks to build it. If he has 8 logs that can make five woodblocks each, how many logs does the carpenter still need?

Sasha completes 15 questions / hour * 2 hours = 30 questions. This means there are still 60 questions 30 questions = 30 questions left to complete.
The answer: 30
Reverse engineering the question: Sasha can complete 15 questions an hour. If she has 60 questions to complete and she works for 2 hours, how many questions does she still need to complete?

Let N be the original price each friend was going to pay. 10N = 6(N + 8). 10N = 6N + 48. 4N = 48. N = 12. Then the present costs 10 * 12 = 120.
The answer: 120
Reverse engineering the question: Ten friends decide to get an end-of-year gift for their teacher. They plan to split the cost of the gift equally. But four of the group drop out. The remaining friends split the cost equally among themselves. If each share is now $8 more, how much does the gift cost, in dollars?

Let x represent the number of true / false questions. Free response:x + 7. Multiple choice: 2(x + 7) = 2x + 14. Total:x + x + 7 + 2x + 14 = 45. 4x + 21 = 45. 4x = 24. x = 6 true / false questions.
The answer: 6
Reverse engineering the question:
Stacy is a high school Calculus teacher. She assigns 45 problems for homework. There are twice as many multiple choice problems as free response, and 7 more free response than true/false. How many true/false questions are there?