The total number of light bulbs in the 20 lamps is 20 * 7 = 140. If 1 / 4 of the 20 lamps have burnt - out light bulbs, there are 1 / 4 * 20 = 5 lamps with burn out light bulbs. Since each of the 5 lamps has 2 burnt - out light bulbs, the number of burn out light bulbs is 2 * 5 = 10. The number of working light bulbs is 140 - 10 = 130.
The answer: 130
Reverse engineering the question: Reyna had 20 lamps with seven light bulbs in each lamp. If 1/4 of them have 2 burnt-out light bulbs each, how many light bulbs are working?


Reasoning and answer: There were 12.6 - 4.6 = 8 gigabytes used after deleting some files. Then, the used space went up to 8 + 2 = 10 gigabytes after storing other files. Thus, the new 20 gigabytes external drive will have 20 - 10 = 10 gigabytes free.
The answer: 10
What was the question?
Question: Sarah's external drive showed 2.4 gigabytes free and 12.6 gigabytes used. She decided to delete a folder of size 4.6 gigabytes and store new files of 2 gigabytes. If she will transfer all her files to a new external drive of size 20 gigabytes, how many free gigabytes will the new external drive have?


A whole pea patch is 5 * 6 = 30 square feet. A radish patch is 30 / 2 = 15 square feet.
The answer: 15
Reverse engineering the question: A pea patch is twice as big as a radish patch. If one sixth of the pea patch is 5 square feet. How much is a whole radish patch in square feet?


Reasoning and answer: If Luke is 20, he will be 20 + 8 = 28 years old in eight years. In eight years, Mr. Bernard will be 3 times as old as Luke is now, a total of 3 * 20 = 60 years old. Mr. Bernard is now 60 - 8 = 52 years old. The sum of their current ages is 52 + 20 = 72. Their average age is 72 / 2 = 36. 10 less than their average age is 36 - 10 = 26 years.
The answer: 26
What was the question?
Question: In eight years, Mr. Bernard will be 3 times as old as Luke is now. If Luke is 20, what is 10 years less than their average age?


Each basket contains an average of 25 fruits so the 5 baskets in all contain 25 * 5 = 125 fruits. The number of apples, mangoes, peaches and pears is 15 + 30 + 20 + 25 = 90. The remaining fruits are bananas and they are 125 - 90 = 35 in number.
The answer: 35
Reverse engineering the question: The average number of fruits per basket in five baskets is 25. If basket A contains 15 apples, B has 30 mangoes, C has 20 peaches, D has 25 pears and E has some bananas, how many bananas are in basket E?


The three students want a total of 3 + 2 + 5 = 10 pencils. Each pencil cost 20 cents so 10 pencils cost 20 * 10 = 200 cents. 100 cents make a dollar so 200 cents make 200 / 100 = 2 dollars.
The answer: 2
Reverse engineering the question:
Some students want to buy pencils from a stationery shop. The price of one pencil is 20 cents. Tolu wants 3 pencils, Robert wants 5 pencils and Melissa wants 2 pencils. How much (in dollars) will the students spend altogether at the stationery shop?