SAT Math Multiple Choice Practice Question 111: Answer and Explanation

Next steps

Question: 111

1. Which of the following equations has 3 as a solution?

I.x2 - 9x = 0

II.x2 + x - 12 = 0

III.x2 + 6x + 9 = 0

A. I only
B. II only
C. III only
D. I and II
E. II and III

Correct Answer: B

Explanation:

B. The first equation factors to x(x - 9) = 0, the second to (x + 4)(x - 3) = 0, and the third to (x + 3)(x + 3) = 0. Therefore, the first has solutions of 0 and 9, the second of -4 and 3, and the third of -3 and -3. Two traps await you here. First, lots of people accidentally factor the first equation into (x + 3)(x - 3), but that's x2 - 9, not x2 - 9x. The second trap is forgetting that the roots are the opposite of the factors, so 3 isn't a solution to the third equation.

Previous       Next