a) Explain the main characteristics of the normal distribution. (4 marks) Terangkan ciri-ciri utama taburan normal. b) The volume of sales of a company have a mean of 20,000 units per month with a standard deviation of 3,000 units per month. You may assume that sales are normally distributed. Find the probability that the volume of sales per month will be: Jumlah jualan syarikat yang mempunyai min sebanyak 20,000 unit sebulan dengan sisihan piawai 3,000 unit sebulan. Anda boleh menganggap bahawa jualan adalah bertaburan normal. Cari kebarangkalian bahawa jumlah jualan bagi setiap bulan adalah: i) less than 15,000 kurang daripada 15,000 ii) between 15,300 and 23,000 antara 15,300 dan 23,000 iii) over 23,000 melebihi 23,000 (8 marks) c) The accountants report that for sales of 23,000 or over, the profit generated is RM25,000; for sales between 15,300 and 23,000, the profit generated is RM8,000 and for sales less than 15,000, there is a loss of RM20,000. Calculate the expected net profit..