PSAT Math Grid-Ins Question 126: Answer and Explanation

Question: 126

Given that (x, y) is a solution to the following system of equations, what is the sum of x and y?
2x – y = 3
4y = 6x

Correct Answer: 15

Explanation:

15 Solve the second equation for y to solve this system of equations using substitution:

Next, plug in x for y in the first equation:

In order to combine the x-terms, you need a common denominator:

So our equation becomes x = 3. Dividing both sides by tells you that x = 6. Next, plug in 6 for x in the equation that you already solved for y:

Since x = 6 and y = 9, their sum is 6 + 9 = 15.