Automobiles traveling on a road with a posted speed limit of 65 miles per hour are checked for speed by a state police radar system. The following is a frequency distribution of speeds.

Speed (miles per hour)Frequency45 up to 555055 up to 6532565 up to 7527575 up to 8525(See the Excel Data File.)

The standard deviation of this distribution is the closest to ________. 10.25

9.54

6.81

5.35