PSAT Math Multiple-Choice Question 481: Answer and Explanation

Question: 481

2a – b = 11

4a – b = 7

What is the value of a if the solution to the system of equations above is (a, b)?

• A. 4
• B. 6
• C. –2
• D. –15

Correct Answer: C

Explanation:

C

The question asks for the value of a variable in a system of equations. Since the question asks for a, look for a way to eliminate b. Multiply the first equation by –1 so that the b terms will have the same coefficient with opposite signs. The new version of the first equation becomes –2a + b = –11. Keep the second equation as 4a – b = 7. Stack and add the two equations together.

Divide both sides by 2 to get a = 2. The correct answer is (C).