The following grouped frequency distribution represents the length of service in years of employees who have been working for a company for at least ten years. Class Boundaries deaf mar " Frequency And doplayed 10-15 30 15-20 42 20-25 23 25-30 13 30-35 35-40 40-45 NNA 45-50 Find the mean, modal class, variance and standard deviation. USE GRAPHING CALCULATOR