Mathematics > Standard Multiple Choice
Read the following SAT test question and then click on a button to select your answer.
If a - b = b - 3 = 6, what is the value of a?
(A) -3
(B) 6
(C) 9
(D) 15
(E) 18
The Correct answer is D.
Explanation
Both a - b = 6 and b - 3 = 6. The equation a - b = 6 cannot be solved for a because there are two unknowns. The value of b can be found by solving the equation for b - 3 = 6. It follows that b must equal 9. The value of b can now be substituted into the equation a - b = 6 , giving a - 9 = 6. Therefore, a must equal 15.
