A doctor created the following frequency distribution summarizing how often her patients visited her office during the last year. Number of visits Number of during the last year patients 1 - 3 4 4- 6 5 7-9 5 10 - 12 8 13 - 15 3 Use this frequency distribution to approximate the standard deviation of the number of times an individual patient visited the office during the last year. Treat the data as population data. Round your answer to two decimal places