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Q7 (8 points) According to the records of an electric company serving the Boston, USA are the mean electricity consumption during winter for all households is 1650 kilowatt-hours per month Assume that the monthly electric consumptions during winter by all households in this area a normal distribution with a mean of 1650 kilowatt-hours and a standard deviation of 320 kilowatt-hours. Answer the following: (a) (4 marks) What percentage of customers have electricity consumption less than 1900 kilowatt hours during the winter? (b) (4 marks) Determine the 90th percentile of all electricity consumption kilowatt-hours during the winter within the Boston area