When the price of the book is decreased by 15%, the total price decrease is 15 / 100 * $400 = $60. The new price of the book becomes $400 - $60 = $340. The price of the book is then increased by 40 / 100 * 340 = $136. The final price of the book is $340 + $136 = $476.
The answer: 476
Reverse engineering the question: The price of a book was $400. If the book's price is decreased by 15% and then increased by 40%, what is the final price of the book?

8 x 2 = 16 are blue pens. 16 + 10 = 26 are black pens. 8 - 2 = 6 are red pens. Therefore, there are 16 + 26 + 6 = 48 pens in all in Sam's collection.
The answer: 48
Reverse engineering the question: In Sam's collection, there are ten more black pens than blue pens and twice as many blue pens as pencils. There are also eight pencils and two fewer red pens than pencils. How many pens in all are there in Sam's collection?

There are approximately 4 weeks in a month. The shop owner added 3 bikes every week for 4 weeks for a total addition of 3 * 4 = 12 bikes. The shop owner now has the original number of bikes + 12 bikes. She sold 18 bikes within the same time frame. She now has a total of 45 bikes which is: the original number of bikes + 12 - 18 = 45 bikes. The original number of bikes = 45 - 12 + 18 = 51 bikes.
The answer: 51
Reverse engineering the question: A bicycle shop owner adds 3 bikes to her stock every week. After 1 month, she had sold 18 bikes but still had 45 bikes in stock. How many bikes did she have originally?

Ernesto = 11 + 3 = 14. Jayden = 14 / 2 = 7 in 3 years. Now = 7 - 3 = 4. Jayden is 4 years old.
The answer: 4
Reverse engineering the question:
In 3 years, Jayden will be half of Ernesto's age. If Ernesto is 11 years old, how many years old is Jayden now?