kris works in the mailroom of a large company and is responsible for all letters sent by the company. the weight of the letters are sent by the company, W grams, have normal distribution with meean 165g and standard deviation 35g estimate the proportions of the letters seent by the company that weight less than 120g kris splits the letters to be sent into 3 categories: heavy, medium and light with 1/3 of the letters in each category find the weight limits that determine medium leters