Solve the system: 2x + y = 7 and x - y = 1. What is x?

Solve the system: 2x + y = 7 and x - y = 1. What is x?

• A. 3
• B. 4
• C. 2
• D. 8/3

Answer: (D)

Eliminate a variable by adding the equations: (2x + y) + (x − y) = 7 + 1, which leaves 3x = 8. So x = 8/3. You can also solve by substitution: from the second equation y = x − 1, plug into the first to get 2x + (x − 1) = 7, which again gives 3x = 8 and x = 8/3. Therefore, x is 8/3.

Eliminate a variable by adding the equations: (2x + y) + (x − y) = 7 + 1, which leaves 3x = 8. So x = 8/3. You can also solve by substitution: from the second equation y = x − 1, plug into the first to get 2x + (x − 1) = 7, which again gives 3x = 8 and x = 8/3. Therefore, x is 8/3.