The Following Is the Frequency Distribution for the Speed of a Sample

Multiple Choice

The following is the frequency distribution for the speed of a sample of automobiles traveling on an interstate highway. $$\begin{array} { c c } \text { Speed } ( m p h ) & \text { Frequency } \\50 - 54 & 2 \\55 - 59 & 4 \\60 - 64 & 5 \\65 - 69 & 10 \\70 - 74 & 9 \\75 - 79 & \underline { 5 } \\& 35\end{array}$$ The standard deviation is

A) 6.969.
B) 7.071.
C) 48.570.
D) 50.000.