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A walk-in clinic for emergency room services maintains Number of Patients per Day Frequency records of the number of patients it treats per day. The following table shows the frequency of the patient arrivals 20 to under 40 15 over the course of a 161-day period. 40 to under 60 13 a. Calculate the approximate average number of 60 to under 80 22 patients per day. b. Calculate the approximate variance and standard 80 to under 100 75 deviation of the number of patients per day. 100 to under 120 36