SAT Math Multiple Choice Question 225: Answer and Explanation
15. 4a + 2z = 10
-3a + z = -10
Based on the system of equations above, what is the value of 10a ?
- A. -10
- B. -1
- C. 3
- D. 30
Correct Answer: D
D Whenever there are two equations with the same two variables, they can be solved simultaneously by adding or subtracting them. The key is to get one variable to disappear. Multiply the second equation by -2, to get 6a - 2z = 20. Stack the two equations and add them.
Therefore, the correct answer is (D). Be careful of (C)-the question did NOT ask for the value of a.