The test scores of a group of students are shown on the cumulative frequency graph below. 200 180 160 140 120 Cumulative frequency 40 20 - 0 - 0 10 20 30 40 50 60 70 80 90 100 Test Scores (a) Estimate the median test score. (1) (b) The top 10 % of students receive a grade A and the next best 20 % of students receive a grade B. Estimate (i) the minimum score required to obtain a grade A: (ii) the minimum score required to obtain a grade B. (4) (Total 5 marks)