First find the total number of minnows by dividing the number of red minnows by the percentage of minnows that are red: 20 minnows / 40% = 50 minnows. Then subtract the percentages of red - and green - bellied minnows to find the percentage of white - bellied minnows: 100% - 40% - 30% = 30%. Then multiply the total number of minnows by the percentage that have white bellies: 30% * 50 minnows = 15 minnows.
The answer: 15
Reverse engineering the question: Mary is counting the number of minnows in the pond. 40% of the minnows have red bellies, 30% have green bellies and the rest have white bellies. If 20 minnows have red bellies, how many minnows have white bellies?


Reasoning and answer: The first 3 ducklings find 3 x 5 = 15 snails. The next 3 ducklings find 3 x 9 = 27 snails. They find a total of 15 + 27 = 42 snails. Mother duck finds 42 x 3 = 126 snails. The last group has 8 - 3 - 3 = 2 ducklings. They find 126 / 2 = 63 snails each. The family of ducks found a total of 42 + 126 + 63 + 63 = 294 snails.
The answer: 294
What was the question?
Question: A mother duck as 8 ducklings. The first 3 ducklings find 5 snails each. Another 3 ducklings find 9 snails each, and the remaining ducklings each find half the number of snails that mother duck finds. If mother duck finds tree times the total number of snails as the first 2 groups of ducklings, how many snails does the family of ducks have collectively?


Eric has a total of 12 + 6 = 18 white and blue marbles. Thus, he has 20 - 18 = 2 green marbles.
The answer: 2
Reverse engineering the question: Eric has 20 marbles. He has 12 white marbles, 6 blue marbles, and the rest are green marbles. How many green marbles does Eric have?


Reasoning and answer: Tim has 68 - 30 = 38 apples. Harry has 38 / 2 = 19 apples.
The answer: 19
What was the question?
Question: Tim has 30 less apples than Martha, and Harry has half as many apples as Tim. If Martha has 68 apples, how many apples does Harry have?


Meena bakes a total of 5 x 12 = 60 cookies. Mr. Stone buys 2 x 12 = 24 cookies. Brock buys 7 cookies, so Katy buys 2 x 7 = 14 cookies. Meena sells a total of 24 + 7 + 14 = 45 cookies. She has 60 - 45 = 15 cookies left.
The answer: 15
Reverse engineering the question: Meena bakes 5 dozen cookies for the school’s bake sale. She sells 2 dozen cookies to her biology teacher, Mr. Stone. Her friend Brock buys 7 cookies, and her friend Katy buys twice as many as Brock. How many cookies does Meena have left?


At the end of 2018, the tree will grow 100 x 10 / 100 = 10 meters more. Thus, its height at the end of 2018 is 100 + 10 = 110 meters. At the end of 2019, the tree will grow 110 x 10 / 100 = 11 meters more. So, its height at the end of 2019 is 110 + 11 = 121 meters. Therefore, the tree has grown 121 - 100 = 21 meters.
The answer: 21
Reverse engineering the question:
A certain tree was 100 meters tall at the end of 2017. It will grow 10% more than its previous height each year. How long has the tree grown from 2017 until the end of 2019?