SAT Math Multiple Choice Practice Question 35: Answer and Explanation
13. If ab = n, b + c = x, and n ≠ 0, which of the following must equal n?
A. ax + c
B. ax - c
C. ax - ac
D. ax - cx
E. ac - ax
Correct Answer: C
C. Because b + c = x, b = x - c. So you can substitute (x - c) for b in the first equation, and write a(x - c) = n. Because of the parentheses, you have to use the distributive law to get ax - ac = n, which is Choice (C).