WAEC Mathematics 2011 Paper

Concept:Total earnings equal the number of correct answers multiplied by the amount earned per correct answer.Explanation:Let the number of correctly answered questions be $n$.The amount earned for each correct answer is $D(n + 50)$.His total earnings are $D600.00$.So, $n \times (n + 50) = 600$.Expand the equation:$n^2 + 50n = 600$$n^2 + 50n - 600 = 0$Factorise the quadratic:$(n + 60)(n - 10) = 0$Thus, $n = -60$ or $n = 10$.Since the number of questions cannot be negative, $n = 10$.Answer:The student answered 10 questions correctly. Option D.