SAT Math Multiple Choice Question 498: Answer and Explanation

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Question: 498

3. Red tide is a form of harmful algae that releases toxins as it breaks down in the environment. A marine biologist is testing a new spray, composed of clay and water, hoping to kill the red tide that almost completely covers a beach in southern Florida. He applies the spray to a representative sample of 200 square feet of the beach. By the end of the week, 184 square feet of the beach is free of the red tide. Based on these results, and assuming the same general conditions, how much of the 10,000-square-foot beach would still be covered by red tide if the spray had been used on the entire area?

  • A. 800 sq ft
  • B. 920 sq ft
  • C. 8,000 sq ft
  • D. 9,200 sq ft

Correct Answer: A



Difficulty: Medium

Category: Problem Solving and Data Analysis / Statistics and Probability

Strategic Advice: This is a science crossover question. Read the first two sentences quickly—they are simply describing the context of the question. The last two sentences pose the question, so read those more carefully.

Getting to the Answer: In the sample, 184 out of 200 square feet were free of red tide after applying the spray. This is of the area. For the whole beach, 0.92(10,000) = 9,200 square feet should be free of the red tide. Be careful—this is not the answer. The question asks how much of the beach would still be covered by red tide, so subtract to get 10,000 - 9,200 = 800 square feet.

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