WAEC Mathematics 2018 Paper

Concept:Inverse variation means one quantity increases as the other decreases.Here, $y$ varies inversely as the square of $x$, so $y = \dfrac{k}{x^2}$.Explanation:Start with the general equation for inverse square variation:$$y = \frac{k}{x^2}$$Substitute $x = 3$ and $y = 100$ to find $k$:$$100 = \frac{k}{3^2}$$$$100 = \frac{k}{9}$$Multiply both sides by $9$:$$k = 100 \times 9 = 900$$Now put $k = 900$ back into the general equation:$$y = \frac{900}{x^2}$$Multiply both sides by $x^2$ to get the required equation:$$yx^2 = 900$$Answer:The equation connecting $x$ and $y$ is $yx^2 = 900$.Correct option: B. $yx^2 = 900$