Arnold owns three cars. The first car averages 50 miles per gallon of gas. The second car averages 10 miles per gallon of gas. And the third car averages 15 miles per gallon of gas. He splits his 450-mile monthly driving mileage equally amongst his three cars. If gas costs $2 per gallon, how much does he spend on gas each month? Give the rationale and then the answer.
Let's think step by step. He drives each vehicle 150 miles because 450 / 3 = 150. The first car will need 3 gallons of gas because 150 / 50 = 3. The second car will need 15 gallons of gas because 150 / 10 = 15. The third car will need 10 gallons of gas because 150 / 15 = 10. He will need 28 gallons in total because 3 + 15 + 10 = 28. This will cost him $56 because 28 x $2 = $56.. The answer is: 56.

In 2004, there were some kids at a cookout. In 2005, half the number of kids came to the cookout as compared to 2004. In 2006, 2/3 as many kids came to the cookout as in 2005. If there were 20 kids at the cookout in 2006, how many kids came to the cookout in 2004? Give the rationale and then the answer.
Let's think step by step. In 2005, 20 / 2 * 3 = 30 kids came to the cookout. In 2004, 30 * 2 = 60 kids came to the cookout.. The answer is: 60.

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? Give the rationale and then the answer.

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
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Let's think step by step. 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 is: 15.