SAT Math Multiple Choice Practice Question 532: Answer and Explanation
10. If x2 – x = 12 and y2 – y = 12, what is the greatest possible value of x – y ?
Correct Answer: C
C Here's a good rule of thumb for the SAT: If it looks like a quadratic equation, try to make it into a quadratic equation. If you try to solve for x, the best way is to move 12 to the same side of the equation, and then factor. x2 – x – 12 = 0 will factor as (x – 4)(x + 3). This means that x could be 4 or –3. You can factor for y in the same way, so y could also be 4 or –3. The greatest value for x – y will be if x = 4 and y = –3, which is a difference of 7.