Each Person Who Applies for an Assembly Job at Robert's

Multiple Choice

Each person who applies for an assembly job at Robert's Electronics is given a mechanical aptitude test. One part of the test involves assembling a plug-in unit based on numbered instructions. A sample of the length of time it took 42 persons to assemble the unit was organized into the following frequency distribution. What is the standard deviation (in minutes) ?

A) 3.89
B) 6.01
C) 8.78
D) 17.00
E) Zero