2x - y = 8x + 2y = 4For the system of equations above, what is the value of x + y?
Correct answer: B. 4
- A. -1
- B. 4
- C. 5
- D. 20
Explanation
Choice B is correct. Multiplying both sides of the first equation in the system by 2 yields 4x − 2y = 16. Adding 4x − 2y = 16 to the second equation in the system yields 5x = 20. Dividing both sides of 5x = 20 by 5 yields x = 4. Substituting 4 for x in x + 2y = 4 yields 4 + 2y = 4. Subtracting 4 from both sides of 4 + 2y = 4 yields 2y = 0. Dividing both sides of this equation by 2 yields y = 0. Substituting 4 for x and 0 for y in the expression x + y yields 4 + 0 = 4.
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