JAMB Mathematics 2012 Paper

Concept:A pie chart represents the whole group as $360^\circ$, so each sector angle gives the fraction of students in that grade.Explanation:The excellent sector is the part of the pie chart not labelled with the other grades.Add the given angles:$$120^\circ + 90^\circ + 80^\circ = 290^\circ$$So the angle for excellent is:$$360^\circ - 290^\circ = 70^\circ$$The fraction of students with excellent is $\frac{70}{360}$.Multiply this fraction by the total number of students, $36$:$$\frac{70}{360} \times 36 = 7$$Thus, 7 students scored excellent.Answer:$7$ students.