SAT Math Multiple Choice Question 816: Answer and Explanation

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Question: 816

6. Body mass index (BMI) is a comparison of a person's body mass to his or her height.A high BMI can be an indicator of high body fat, which can lead to health problems.According to the American Heart Association, an adult is underweight if his or herBMI is less than 18.5, or overweight if it is greater than or equal to 25.0. Whichof the following number lines could be used to model a healthy BMI range for an adult?

  • A.
  • B.
  • C.
  • D.

Correct Answer: A

Explanation:

A

Difficulty: Medium

Category: Heart of Algebra / Inequalities

Strategic Advice: When you see phrases like "less than" or "greater than," write an inequality to describe the situation. Then graph your inequality on a number line by shading to the left for < or ≤ and shading to the right for > or ≥.

Getting to the Answer: A person with a BMI that is less than 18.5 is underweight. If b represents BMI, the BMI of an underweight person can be expressed as b < 18.5, so draw an open dot at 18.5 and shade to the left. Likewise, a person with a BMI that is greater than or equal to 25.0 is overweight, which can be expressed as b ≥ 25.0. Draw a solid dot at 25 and shade to the right. The number line in choice B represents the combination of these inequalities, but be careful-that's not what the question asks! The question asks for the healthy BMI range, so you're looking for the opposite of choice B-a solid dot at 18.5, an open dot at 25.0, and shaded between them, which is (A).

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