The new camera cost 4000 * .3 = $1200 more than the old camera. So the camera cost 4000 + 1200 = $5200. The lens cost 400 - 200 = $200. So the total cost was 5200 + 200 = $5400.
The answer: 5400
Reverse engineering the question: Mike decides to buy a new camera. He wants to buy a top-of-the-line camera but he decides to wait for the new model to come out. The new model costs 30% more than the current model. The old camera cost $4000. He gets $200 off a $400 lens he bought. How much did he pay for the camera and lens?


Reasoning and answer: Onum lake has 25 trout + 75 = 100 fish. Riddle Pond has 1 / 2 * 100 fish in Onum lake = 50 fish. Combined the three bodies of water have 100 fish + 50 fish + 75 fish = 225 fish. The average number of fish in the bodies of water is 225 fish / 3 = 75 fish.
The answer: 75
What was the question?
Question: Onum Lake has 25 more trout than Boast Pool.  There are 75 fish in Boast Pool. Riddle Pond has half as many fish as Onum Lake. What is the average number of fish in all three bodies of water?


The doctor charged 300 / 2 = $150. So the total cost was 150 + 150 + 1200 = $1500. The insurance covered 1500 * .8 = $1200. So he paid 1500 - 1200 = $300.
The answer: 300
Reverse engineering the question: Tim has to go to the doctor for a sporting injury. He gets an MRI which costs $1200. The doctor needs to examine it for 30 minutes and charges $300 per hour. There is also a $150 fee just for being seen. Insurance covered 80% how much did he pay?


Reasoning and answer: The school prepared 40 x 20 = 800 chairs. So, 800 - 10 = 790 chairs were taken.
The answer: 790
What was the question?
Question: For the school play, 40 rows of chairs were set up where there were 20 chairs in each row. If only 10 seats were not occupied, how many seats were taken?


Wilson had $150 + $17 = $167 two months ago before making a withdrawal. His money in his account now is $150 + $16 = $166. Since he deposited $21 this month, this means there was $166 - $21 = $145 last month after making a withdrawal. Therefore, Wilson withdrew $167 - $145 = $22.
The answer: 22
Reverse engineering the question: Two months ago, Wilson had a total of $150 in his bank account. Then last month, he deposited $17. A few days after, he made a withdrawal. This month, he deposited $21 so he has $16 more than what is in his account two months ago. How much did Wilson withdraw last month?


After half an hour, the number of balloons that had blown up is 1 / 5 * 200 = 40. The number of balloons that haven't blown up so far is 200 - 40 = 160. In the next hour, 2 * 40 = 80 balloons blow up. The number of balloons that haven't blown up now is 160 - 80 = 80.
The answer: 80
Reverse engineering the question:
A hot air balloon with 200 balloons is blowing up. After about half an hour, 1/5 of the total number of balloons in the hot air balloon have blown up. After another hour, twice the number of balloons that had already blown up also blow up. How many balloons in the hot air balloon remain intact?