PSAT Math Multiple-Choice Question 139: Answer and Explanation

Question: 139

The total surface area of the triangular prism shown above can be calculated using the following formula, where x is the length of the sides of the triangular ends and y is the length of the rectangular faces.

What must the expression represent?

• A. The area of one triangular end
• B. The area of one rectangular face and one triangular end
• C. The sum of the areas of the rectangular faces
• D. The sum of the areas of the triangular ends

Correct Answer: D

Explanation:

D

The question asks for the meaning of an expression in context. Start by reading the final question, which asks for the meaning of the expression . Then label the parts of the equation with the information given. The question states that x is the length of the sides of the triangular ends and y is the length of the rectangular faces. The equation becomes . Next, use Process of Elimination to get rid of answer choices that are not consistent with the labels. Since the expression only includes the sides of the triangular faces as a variable, it doesn't refer to the rectangular faces; eliminate (B) and (C). Compare the remaining answer choices. The difference between (A) and (D) is the number of triangular faces included. In the equation, the term is multiplied by 2, which would result in . Therefore, must represent both the triangular sides. Eliminate (A). The correct answer is (D).