PSAT Math Multiple-Choice Question 315: Answer and Explanation

Question: 315

The graph above shows the volume of a sample of gas as it is cooled. If T is the temperature of the gas in degrees Celsius and V is the volume in liters, which of the following equations, when plotted, could produce the graph shown?

• A. V = 0.004T + 100
• B. V = 0.004T
• C. V = 0.004T + 1
• D. V = 0.004T - 0.25

Correct Answer: C

Explanation:

C

Difficulty: Medium

Getting to the Answer: Temperature, T, is the independent variable on the x-axis, and volume, V, is the dependent variable on the y-axis. Therefore, the skeleton of the equation you're looking for is V = mT + b. Because each answer choice has a different y-intercept, finding b is enough to get the correct answer; there is no need to determine the slope. Although the graph is not centered around the origin, you can still find the y-intercept. In this case, it's 1. This eliminates every answer choice except (C), which is correct.