# SAT Math Multiple Choice Question 771: Answer and Explanation

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**Question: 771**

**6.** If the variable *a* varies inversely as *b*, which of the following statements must be true?

- A.
*a*+*b*is a constant. - B.
*a*-*b*is a constant. - C. is a constant.
- D.
*ab*is a constant.

**Correct Answer:** D

**Explanation:**

**D**

**Problem Solving and Data Analysis (variation) MEDIUM-HARD**

Recall from Chapter 8, Lesson 4, that if *a* is inversely proportional to *b*, then , where *k* is some positive constant. If we multiply both sides of this equation by *b*, we get *ab* = *k*, which means that the product *ab* is a constant.