Algebra practice question

Answer: 3.5 or 7/2

Add the equations to eliminate y: 4x = −4, so x = −1. Substitute into x − 2y = −8: −1 − 2y = −8, so −2y = −7 and y = 7/2 = 3.5.

Common wrong answers

If you answered -1

−1 is x. The question asks for y.

If you answered -3.5

−3.5 has the wrong sign: from −1 − 2y = −8, −2y = −7, so y = +3.5.

If you answered 2.5

2.5 would come from x = 1 (a sign slip in 4x = −4). x is −1.

More Algebra questions

• Medium
  A system: 2x + y = 11 and x − y = 1. What is the value of x + y?
• Medium
  Which of the following describes all solutions to 4x − 9 ≤ 2x + 5?
• Medium
  A phone's battery percentage is modeled by P = 100 − 8t, where t is the number of hours since it was unplugged…
• Medium
  If y = 2x − 1 and 3x + y = 14, what is the value of x?
• Medium
  If |2x − 3| = 7, what is the sum of all possible values of x?
• Medium
  Line k has equation y = (2/3)x + 1. Which equation represents a line perpendicular to line k?