SAT Math Multiple Choice Question 115: Answer and Explanation

Home > SAT Test > SAT Math Multiple Choice Practice Tests

Test Information

Question: 115

10. 2c + 3d = 17
6c + 5d = 39

In the system of linear equations above, what is the value of 4c - 4d ?

  • A. -4
  • B. 1
  • C. 4
  • D. 13

Correct Answer: C

Explanation:

C We must find values of c and d by solving the system of equations in order to determine the value of 4c - 4d. There are several ways to go about this. One way is to multiply the terms of the equation 2c + 3d = 17 by -3 to get -6c - 9d = -51 . If you stack and add this equation with the second equation, the result is -4d = -12, which solves to d = 3. Plug this value for d into the equation 6c + 5d = 39 to get 6c + 15 = 39, so 6c = 24 and c = 4. Therefore, 4c - 4d = 4(4) - 4(3) = 16 - 12 = 4. This is (C).

Previous       Next