15. A quiz marked out of 100 is written by 800 students. The cumulative frequency graph for the marks is given below. 800 700 600 500 400 300 200 Number of candidates 100 0 10 20 30 40 50 60 70 80 90 100 Mark a) Estimate the number of students who scored 25 marks or less on the quiz. b) The middle 50% of the quiz results lie between marks a and b, where a < b. Find the values of a and b. 16. Consider the data set {k 3, k, k + 2, k + 5}, where k R. a) Find the mean of this data set in terms of k. Each number in the above data set is now decreased by 3. b) Find the mean of this new data set in terms of k. 17. 200 vehicles are tested for their air pollution efficiency. The results are given in the cumulative frequency graph 200 180 Cumulative frequency 120- 100 642886420 0 10 20 30 40 50 60 70 80 90 100 Test scores a) Estimate the median test score. b) The top 10% of the vehicles receive a lower insurance premium price A and the next best 20% of the vehicles receive a price B. Estimate i) the minimum score required to obtain price A iii) the minimum score required to obtain a price B.