6 builders can build a single floor 6 builders / 3 builders = 2 times as fast as 3 builders. Thus 6 builders would build a single floor in 30 days / 2 = 15 days. There are 5 hours x 6 floors / house = 30 floors in total in 5 houses with 6 floors each. Therefore 6 builders would complete the project in 15 days / floor x 30 floors = 450 days. It would cost 450 days x $100 / day / builder * 6 builders = $270000 to complete the project.
The answer: 270000
Reverse engineering the question: Three builders build a single floor of a house in 30 days. If each builder is paid $100 for a single day's work, how much would it cost to hire 6 builders to build 5 houses with 6 floors each?

If the number of dimes is 20 times the number of quarters, she has 350 / 5 = 70 quarters. When she puts 2 / 5 of the quarters away, the number of quarters reduces by 2 / 5 * 70 = 28. She's now left with 70 - 28 = 42 quarters. In total, she has 42 quarters + 350 dimes = 392.
The answer: 392
Reverse engineering the question: Gloria has five times as many dimes as quarters in her graduation money. She decides to put 2/5 of the quarters aside for future use. If she has 350 dimes, calculate the combined number of quarters and dimes she has after putting aside 2/5 of the quarters?

On Monday, Mr Castiel ate 2 / 5 * 600 = 240 sausages. The remaining number of sausages after he ate 240 on Monday is 600 - 240 = 360. On Tuesday, he ate half of the remaining sausages, a total of 360 / 2 = 180. The remaining number of sausages that he saved for Friday after eating 180 on Tuesday is 360 - 180 = 180. On Friday, Mr Castiel ate 3 / 4 * 180 = 135 of the sausages he had kept. The remaining number of sausages after he ate 135 on Friday is 180 - 135 = 45.
The answer: 45
Reverse engineering the question: Mr Castiel prepared 600 boar sausages on the weekend. He ate 2/5 of them on Monday, half of the remaining on Tuesday and saved the rest for Friday. If he ate 3/4 of the remaining boar sausages on Friday, how many sausages are left?

Carlos memorized 24 / 6 = 4 digits of pi. Sam memorized 4 + 6 = 10 digits of pi.
The answer: 10
Reverse engineering the question:
Sam memorized six more digits of pi than Carlos memorized. Mina memorized six times as many digits of pi as Carlos memorized. If Mina memorized 24 digits of pi, how many digits did Sam memorize?