SAT Math Multiple Choice Question 534: Answer and Explanation

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Question: 534

9. Ethanol is an alcohol commonly added to gasoline to reduce the use of fossil fuels. A commonly used ratio of ethanol to gasoline is 1:4. Another less common and more experimental additive is methanol, with a typical ratio of methanol to gasoline being 1:9. A fuel producer wants to see what happens to cost and fuel efficiency when a combination of ethanol and methanol are used. In order to keep the ratio of gasoline to total additive the same, what ratio of ethanol to methanol should the company use?

  • A. 1:1
  • B. 4:9
  • C. 9:4
  • D. 36:9

Correct Answer: C

Explanation:

C

Difficulty: Hard

Category: Problem Solving and Data Analysis / Rates, Ratios, Proportions, and Percentages

Strategic Advice: You're given two ratios: ethanol to gasoline and methanol to gasoline. Your job is to "merge" them so you can directly compare ethanol to methanol.

Getting to the Answer: Both of the given ratios contain gasoline, but the gasoline amounts (4 and 9) are not identical. To directly compare them, find a common multiple (36). Multiply each ratio by the factor that will make the number of parts of gasoline equal to 36 in each:

Ethanol to Gasoline: (1:4) × (9:9) = 9:36

Methanol to Gasoline: (1:9) × (4:4) = 4:36

Now that the number of parts of gasoline needed is the same in both ratios, you can merge the two ratios to compare ethanol to methanol directly: 9:36:4. So the proper ratio of ethanol to methanol is 9:4.

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