74. Automobiles traveling on a road with a posted speed limit of 55 miles per hour are checked for speed by a state police radar system. Following is a frequency distribution of speeds. Speed (miles per hour) 45-49 50-54 55-59 60-64 65-69 70-74 75-79 Frequency 10 40 150 175 75 15 10 Total 475 a. What is the mean speed of the automobiles traveling on this road. b. Compute the variance and the standard deviation. 15. Martinez Auto Supplies has retail stores located in eight cities in California. The price they charge for a particular product in each city are vary because of differing competitive conditions. For instance, the price they charge for a case of a popular brand of motor oil in each city follows. Also shown are the number of cases that Martinez Auto sold last quarter in each city. Excel File: data03-15.xls Compute the average sales price per case for this product during the last quarter? Round your answer to two decimal places