PSAT Math Multiple-Choice Question 645: Answer and Explanation

Question: 645

If you were to graph dollars per shake-up along the x-axis and quantity of shake-ups sold per week at the set price on the y-axis, which of the following would be a property of the function between the values of 3 and 5 dollars?

• A. It would be a decreasing exponential function.
• B. It would be an increasing exponential function.
• C. It would be a decreasing linear function.
• D. It would be an increasing linear function.

Correct Answer: A

Explanation:

(A) We can see from the negative slope that as the quantity of shake-ups increases, price decreases. Therefore, we know that the function will be decreasing, eliminating choices (B) and (D). We can also see that the slope isn't constant. Therefore, it can't be linear, as in choice (C). The graph starts off fairly steep and then it becomes less steep, consistent with exponential decay, as in choice (A).