WAEC 2021 Mathematics · Question 27

If 4x+2y=16 and 6x-2y=4 , find the value of (y-x).

Options

Answer: B. 2

Explanation written with AI and checked against the answer key

Analyze the question: We have two linear equations in x and y. We solve them together (simultaneous equations), then compute y − x. Concept: Because the y-terms are +2y and −2y, adding the two equations eliminates y. Solution: Equation 1: 4x + 2y = 16 Equation 2: 6x − 2y = 4 Add them: (4x + 6x) + (2y − 2y) = 16 + 4 10x = 20 x = 2 Substitute x = 2 into Equation 1: 4(2) + 2y = 16 8 + 2y = 16 2y = 8 y = 4 Check in Equation 2: 6(2) − 2(4) = 12 − 8 = 4 ✓ Now find y − x: y − x = 4 − 2 = 2 Answer: Option B (2). Tip: When the coefficients of one variable are equal and opposite (like +2y and −2y), just add the equations. If they are equal and the same sign, subtract instead. Always check your values in the other equation before choosing an option.

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