WAEC 2018 Mathematics · Question 18

If y + 2x = 4 and y - 3x = -1, find the value of (x + y)

Options

A.3
B.2
C.1
D.-1

Answer: A. 3

Explanation written with AI and checked against the answer key

Analyze the question: We have two linear equations in x and y, and we need x + y. Solving them simultaneously gives both values. Concept: For simultaneous equations, subtract or add the equations to eliminate one variable. Solution: Equation 1: y + 2x = 4 Equation 2: y − 3x = −1 Subtract Equation 2 from Equation 1: (y + 2x) − (y − 3x) = 4 − (−1) 2x + 3x = 5 5x = 5 x = 1 Substitute x = 1 into Equation 1: y + 2(1) = 4 y = 2 Check in Equation 2: y − 3x = 2 − 3 = −1 ✓ Therefore x + y = 1 + 2 = 3 Answer: Option A (3). Tip: When both equations have y with the same coefficient, subtracting eliminates y immediately. Always check your values in the second equation to catch sign errors, especially with negative numbers like −(−1) = +1.

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