WAEC Mathematics 2020 Paper

Concept:Represent the father's age using the son's age, then form the product equation for four years later.Explanation:Let the son's present age be $y$.The man is five times as old as his son, so the man's present age is $5y$.In four years' time:Son's age will be $y + 4$.Man's age will be $5y + 4$.The product of their ages in four years' time is:$$(5y + 4)(y + 4)$$Given that this product equals $340$:$$(5y + 4)(y + 4) = 340$$Expand:$$5y^2 + 20y + 4y + 16 = 340$$Simplify:$$5y^2 + 24y + 16 - 340 = 0$$So:$$5y^2 + 24y - 324 = 0$$Answer:The required equation is $5y^2 + 24y - 324 = 0$, which matches option D.