PSAT Math Multiple-Choice Question 528: Answer and Explanation

Question: 528

Cost of Electricity

Electricity charge	Cost
Supply	6 cents per kilowatt hour
Delivery	3 cents per kilowatt hour

Mark’s electric bill breakdown is shown in the table above. In addition to his electric bill, Mark’s only other apartment expense is $950 a month for rent. The expression C = (0.06 + 0.03)h + 950 shows the cost C, in dollars, of living in the apartment for a month as a function of h, the number of kilowatt hours of electricity used in a month. What does the y-intercept of the graph of this equation represent?

• A. The cost of electricity supply and delivery per kilowatt hour
• B. The cost of electricity supply and rent for a month
• C. The cost of rent for a month
• D. The cost of rent and electricity per kilowatt hour

Correct Answer: C

Explanation:

C

The question asks about the graph of the data representing a certain situation. Label the parts of the equation to determine what they represent. In this question, C represents the cost of living in the apartment for a month and h represents the number of kilowatt hours of electricity used in a month. The y-intercept of a graph is defined as a point where the graph intersects the y-axis, so the y-intercept must relate to cost of living in the apartment. Eliminate (A), since it does not mention the cost of rent. The equation is in y = mx + b form, where b is the y-intercept of a graph, so here the y-intercept is 950. The question states the only other apartment expense is $950 a month for rent. Therefore, the y-intercept represents the cost of rent. The correct answer is (C).